src: conditionalize EAI_ADDRFAMILY

src: conditionalize EAI_ADDRFAMILY

The EAI_ADDRFAMILY constant has been removed from FreeBSD
headers, supposedly because it is deprecated by new RFC
drafts.

Previously GNULIB was providing a replacement because
MinGW lacked it too. The replacement provided for MinGW
was thus being used on FreeBSD too, but with a completely
bogus integer value.

Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>