This is in preparation of moving to OSPFv3 on VPP.
> If no primary address exists for the interface selected, then the
> primary address of the first non-loopback interface that has one will be
> used regardless of this setting.
To to ensure that for IPv4-less transit networks, the loopback address
is chosen, make it the first interface (notably by ensuring that 'lcp
create' for the loopback interfaces comes before that of PHY and
sub-ints).
f01c865c87