gaih_inet: Split simple gethostbyname into its own function

Add a free_at flag in gaih_result to indicate if res.at needs to be
freed by the caller.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: DJ Delorie <dj@redhat.com>
(cherry picked from commit b44389cb)