[lldpmgrd] Fix lldpmgrd issue where it sets the lldp system name to None

[zhenggen-xu]

[lldpmgrd] Fix lldpmgrd issue where it sets the lldp system name to None

• Only check hostname field in key DEVICE_METADATA|localhost of configDB
• If hostname does not exist, don't set lldp system name

Signed-off-by: Zhenggen Xu zxu@linkedin.com

Why I did it

lldpmgrd could set the system name to None incorrectly, which lead to peer to have wrong lldp information.

How I did it

Fix the lldpmgrd.

How to verify it

Before fix:
If loading below config:

{
    "DEVICE_METADATA": {
        "localhost": {
            "bgp_asn": "65100",
            "docker_routing_config_mode": "split",
            "hostname": "sonic-1",
            "hwsku": "Seastone-DX010",
            "mac": "00:e0:ec:3c:0a:16",
            "platform": "x86_64-cel_seastone-r0",
            "type": "LeafRouter"
        },
        "x509": {
            "ca_crt": "/etc/sonic/telemetry/dsmsroot.cer",
            "server_crt": "/etc/sonic/telemetry/streamingtelemetryserver.cer",
            "server_key": "/etc/sonic/telemetry/streamingtelemetryserver.key"
        }
    }
} 

lldp will set the system name to None, see syslog:

Aug 31 05:06:11.172655 lnos-x1-a-asw02 INFO lldp#lldpmgrd[32]: Device Config Opcode: SET Dict {'docker_routing_config_mode': 'split', 'hwsku': 'Seastone-DX010', 'mac': '00:e0:ec:3c:0a:16', 'platform': 'x86_64-cel_seastone-r0', 'bgp_asn': '65100', 'buffer_model': 'traditional', 'default_bgp_status': 'up', 'default_pfcwd_status': 'disable', 'hostname': 'sonic-1', 'type': 'LeafRouter'} Key localhost
Aug 31 05:06:11.172802 lnos-x1-a-asw02 INFO lldp#lldpmgrd[32]: Hostname changed old None, new sonic-1
Aug 31 05:06:11.192924 lnos-x1-a-asw02 INFO lldp#lldpmgrd[32]: Device Config Opcode: SET Dict {'ca_crt': '/etc/sonic/telemetry/dsmsroot.cer', 'server_crt': '/etc/sonic/telemetry/streamingtelemetryserver.cer', 'server_key': '/etc/sonic/telemetry/streamingtelemetryserver.key'} Key x509
Aug 31 05:06:11.192924 lnos-x1-a-asw02 INFO lldp#lldpmgrd[32]: Hostname changed old sonic-1, new None 

admin@lnos-x1-a-asw02:~$ sudo lldpcli show chassis | grep SysName
  SysName:      None

After the fix, if loading the same config:

Aug 31 05:53:38.686509 lnos-x1-a-asw02 INFO lldp#lldpmgrd[35]: Device Config Opcode: SET Dict {'docker_routing_config_mode': 'split', 'hwsku': 'Seastone-DX010', 'mac': '00:e0:ec:3c:0a:16', 'platform': 'x86_64-cel_seastone-r0', 'bgp_asn': '65100', 'buffer_model': 'traditional', 'default_bgp_status': 'up', 'default_pfcwd_status': 'disable', 'hostname': 'sonic-1', 'type': 'LeafRouter'} Key localhost
Aug 31 05:53:38.686509 lnos-x1-a-asw02 INFO lldp#lldpmgrd[35]: Hostname changed old None, new sonic-1
Aug 31 05:53:38.706948 lnos-x1-a-asw02 INFO lldp#lldpmgrd[35]: Device Config Opcode: SET Dict {'ca_crt': '/etc/sonic/telemetry/dsmsroot.cer', 'server_crt': '/etc/sonic/telemetry/streamingtelemetryserver.cer', 'server_key': '/etc/sonic/telemetry/streamingtelemetryserver.key'} Key x509

admin@lnos-x1-a-asw02:~$ sudo lldpcli show chassis | grep SysName
  SysName:      sonic-1
  

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111
• 202205

Description for the changelog

Link to config_db schema for YANG module changes

A picture of a cute animal (not mandatory but encouraged)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

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can we add UT

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