Fix a regression introduced in Nomad 1.9.0 where CNI bridge networking with
IPv6-only interfaces would fail with 'no interface with an address' error.
The issue was that while the code correctly populated the AddressIPv6 field
for IPv6 addresses, several validation checks only examined the Address field
(IPv4), causing IPv6-only configurations to be rejected.
Changes:
- Update interface selection logic in cniToAllocNet to accept interfaces with
either IPv4 or IPv6 addresses (not just IPv4)
- Update fallback logic to check both Address and AddressIPv6 fields
- Update error check to only fail when both IPv4 and IPv6 are missing
- Update AllocNetworkStatus.IsZero() to check AddressIPv6 field
This allows CNI configurations with IPv6-only interfaces to work correctly,
restoring functionality from Nomad 1.8.x.
Fixes#26905
1136fd342c