Allow OVN dynamic IPv4 if only static IPv6 is configured

[MusicDin]

This PR fixes static IPv4 not being allocated if only static IPv6 is set for an OVN nic.

Currently, this does not work as expected. If OVN is instructed to get dynamic IPs, it will generate dynamic IP for both v4 and v6 family.

For example:

$ lxc launch ubuntu:22.04 c1 -n ovn -d eth0,ipv6.address=fd42:1000:1000:1000:a:b:c:d

$ lxc network list-leases ovn
+----------+-------------------+----------------------------------------+---------+
| HOSTNAME |    MAC ADDRESS    |               IP ADDRESS               |  TYPE   |
+----------+-------------------+----------------------------------------+---------+
| c1       | 00:16:3e:21:c4:7f | 10.100.100.2                           | DYNAMIC |
+----------+-------------------+----------------------------------------+---------+
| c1       | 00:16:3e:21:c4:7f | fd42:1000:1000:1000:216:3eff:fe21:c47f | DYNAMIC | << EUI64
+----------+-------------------+----------------------------------------+---------+
| c1       | 00:16:3e:21:c4:7f | fd42:1000:1000:1000:a:b:c:d            | STATIC  |
+----------+-------------------+----------------------------------------+---------+
| ovn.gw   |                   | 10.100.100.1                           | GATEWAY |
+----------+-------------------+----------------------------------------+---------+
| ovn.gw   |                   | fd42:1000:1000:1000::1                 | GATEWAY |
+----------+-------------------+----------------------------------------+---------+

As a result, instance gets sometimes static IPv6 and sometimes the generated one:

$ lxc ls
+------+---------+---------------------+-----------------------------------------------+-----------+-----------+
| NAME |  STATE  |        IPV4         |                     IPV6                      |   TYPE    | SNAPSHOTS |
+------+---------+---------------------+-----------------------------------------------+-----------+-----------+
| c1   | RUNNING | 10.100.100.2 (eth0) | fd42:1000:1000:1000:216:3eff:fe21:c47f (eth0) | CONTAINER | 0         |
+------+---------+---------------------+-----------------------------------------------+-----------+-----------+
                                         ^ Incorrect

However, after restart (when last used IPs are directly set as static IPs), it works as expected:

$ lxc restart c1

$ lxc ls
+------+---------+---------------------+------------------------------------+-----------+-----------+
| NAME |  STATE  |        IPV4         |                IPV6                |   TYPE    | SNAPSHOTS |
+------+---------+---------------------+------------------------------------+-----------+-----------+
| c1   | RUNNING | 10.100.100.2 (eth0) | fd42:1000:1000:1000:a:b:c:d (eth0) | CONTAINER | 0         |
+------+---------+---------------------+------------------------------------+-----------+-----------+

$ lxc network list-leases ovn
+----------+-------------------+-----------------------------+---------+
| HOSTNAME |    MAC ADDRESS    |         IP ADDRESS          |  TYPE   |
+----------+-------------------+-----------------------------+---------+
| c1       | 00:16:3e:21:c4:7f | 10.100.100.2                | DYNAMIC |
+----------+-------------------+-----------------------------+---------+
| c1       | 00:16:3e:21:c4:7f | fd42:1000:1000:1000:a:b:c:d | STATIC  |
+----------+-------------------+-----------------------------+---------+
| ovn.gw   |                   | 10.100.100.1                | GATEWAY |
+----------+-------------------+-----------------------------+---------+
| ovn.gw   |                   | fd42:1000:1000:1000::1      | GATEWAY |
+----------+-------------------+-----------------------------+---------+