add metrics for TX/RX broadcast, multicast, unicasts, CRC error packets

[kakkotetsu]

This PR adds prometheus metrics for TX/RX broadcast, multicast, unicasts, CRC error packets entries.

The following metrics are now exposed.

# HELP junos_interface_receive_broadcasts Received broadcast packets
# TYPE junos_interface_receive_broadcasts gauge
junos_interface_receive_broadcasts{description="",mac="00:26:88:78:6b:03",name="ge-0/0/46",target="ex3200-1"} 5.06705251e+08

# HELP junos_interface_receive_errors_crc Number of CRC error incoming packets
# TYPE junos_interface_receive_errors_crc gauge
junos_interface_receive_errors_crc{description="",mac="00:26:88:78:6b:30",name="ge-0/0/45",target="ex3200-1"} 1

# HELP junos_interface_receive_multicasts Received multicast packets
# TYPE junos_interface_receive_multicasts gauge
junos_interface_receive_multicasts{description="",mac="00:26:88:78:6b:03",name="ge-0/0/46",target="ex3200-1"} 1.054740167e+09

# HELP junos_interface_receive_unicasts Received unicast packets
# TYPE junos_interface_receive_unicasts gauge
junos_interface_receive_unicasts{description="",mac="00:26:88:78:6b:03",name="ge-0/0/46",target="ex3200-1"} 1.093475547e+09

# HELP junos_interface_transmit_broadcasts Transmitted broadcast packets
# TYPE junos_interface_transmit_broadcasts gauge
junos_interface_transmit_broadcasts{description="",mac="00:26:88:78:6b:03",name="ge-0/0/46",target="ex3200-1"} 4.22708706e+08

# HELP junos_interface_transmit_errors_crc Number of CRC error outgoing packets
# TYPE junos_interface_transmit_errors_crc gauge
junos_interface_transmit_errors_crc{description="",mac="00:26:88:78:6b:05",name="ge-0/0/2",target="ex3200-1"} 0

# HELP junos_interface_transmit_multicasts Transmitted multicast packets
# TYPE junos_interface_transmit_multicasts gauge
junos_interface_transmit_multicasts{description="",mac="00:26:88:78:6b:03",name="ge-0/0/46",target="ex3200-1"} 9.96547927e+08

# HELP junos_interface_transmit_unicasts Transmitted unicast packets
# TYPE junos_interface_transmit_unicasts gauge
junos_interface_transmit_unicasts{description="",mac="00:26:88:78:6b:03",name="ge-0/0/46",target="ex3200-1"} 1.246669437e+09

These metrics are based on the output of show interfaces extensive | display xml .
The output of this command is the output of show interfaces statistics detail | display xml with the following additions.

<rpc-reply xmlns:junos="http://xml.juniper.net/junos/12.3R12/junos">
    <interface-information xmlns="http://xml.juniper.net/junos/12.3R12/junos-interface" junos:style="normal">
        <physical-interface>
            <name>ge-0/0/0</name>

            ...snip

            <ethernet-mac-statistics junos:style="verbose">
                <input-bytes>4779885871833</input-bytes>
                <output-bytes>14355870285837</output-bytes>
                <input-packets>24156588355</input-packets>
                <output-packets>31789344367</output-packets>
                <input-unicasts>22993966350</input-unicasts>
                <output-unicasts>29940927110</output-unicasts>
                <input-broadcasts>153380313</input-broadcasts>
                <output-broadcasts>538903016</output-broadcasts>
                <input-multicasts>1009241692</input-multicasts>
                <output-multicasts>1309514241</output-multicasts>
                <input-crc-errors>0</input-crc-errors>
                <output-crc-errors>0</output-crc-errors>
                <input-fifo-errors>0</input-fifo-errors>
                <output-fifo-errors>0</output-fifo-errors>
                <input-mac-control-frames>0</input-mac-control-frames>
                <output-mac-control-frames>0</output-mac-control-frames>
                <input-mac-pause-frames>0</input-mac-pause-frames>
                <output-mac-pause-frames>0</output-mac-pause-frames>
                <input-oversized-frames>0</input-oversized-frames>
                <input-jabber-frames>0</input-jabber-frames>
                <input-fragment-frames>0</input-fragment-frames>
                <input-code-violations>0</input-code-violations>
            </ethernet-mac-statistics>
            <ethernet-autonegotiation>
                <autonegotiation-status>complete</autonegotiation-status>
                <link-partner-status>OK</link-partner-status>
                <link-partner-duplexity>full-duplex</link-partner-duplexity>
                <link-partner-speed>1000 Mbps</link-partner-speed>
                <flow-control>Symmetric</flow-control>
                <local-info>
                    <local-flow-control>Symmetric</local-flow-control>
                    <local-remote-fault>Link OK</local-remote-fault>
                </local-info>
            </ethernet-autonegotiation>
            <pfe-information>
                <destination-slot>0</destination-slot>
            </pfe-information>
            <cos-header/>
            <cos-information>
                <cos-stream-information>
                    <cos-direction>Output</cos-direction>
                    <cos-queue-configuration>
                        <cos-queue-number>0</cos-queue-number>
                        <cos-queue-forwarding-class>best-effort</cos-queue-forwarding-class>
                        <cos-queue-bandwidth>95</cos-queue-bandwidth>
                        <cos-queue-bandwidth-bps>950000000</cos-queue-bandwidth-bps>
                        <cos-queue-buffer>95</cos-queue-buffer>
                        <cos-queue-buffer-bytes>NA</cos-queue-buffer-bytes>
                        <cos-queue-priority>low</cos-queue-priority>
                        <cos-queue-limit>none</cos-queue-limit>
                    </cos-queue-configuration>
                    <cos-queue-configuration>
                        <cos-queue-number>7</cos-queue-number>
                        <cos-queue-forwarding-class>network-control</cos-queue-forwarding-class>
                        <cos-queue-bandwidth>5</cos-queue-bandwidth>
                        <cos-queue-bandwidth-bps>50000000</cos-queue-bandwidth-bps>
                        <cos-queue-buffer>5</cos-queue-buffer>
                        <cos-queue-buffer-bytes>NA</cos-queue-buffer-bytes>
                        <cos-queue-priority>low</cos-queue-priority>
                        <cos-queue-limit>none</cos-queue-limit>
                    </cos-queue-configuration>
                </cos-stream-information>
            </cos-information>

            ...snip

[czerwonk]

Please add a unit to the metric names to make it more clear. Everything else LGTM

[czerwonk]

Please add a unit to the metric name (e.g. _packets)

[kakkotetsu]

Thank you for reviewing it!
Added units to the metric name. (_packets)

[czerwonk]

LGTM