gaih_inet: Simplify service resolution

Refactor the code to split out the service resolution code into a
separate function.  Allocate the service tuples array just once to the
size of the typeproto array, thus avoiding the unnecessary pointer
chasing and stack allocations.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: DJ Delorie <dj@redhat.com>