gai_strerror.[c3]: re-enable EAI_ADDRFAMILY, EAI_NODATA
gai_strerror.c still has messages for EAI_ADDRFAMILY and EAI_NODATA,
but not the man page. Re-add to the man page, and update comments
in the source. Document the errors that are not in RFC 3493 or
Reviewed in https://reviews.freebsd.org/D37139 with related changes.
Reviewed by: bz, pauamma
(cherry picked from commit e34adc71d3724a8b1add483310efbc63db9290a6)