gaih_inet: Simplify canon name resolution

Simplify logic for allocation of canon to remove the canonbuf variable;
canon now always points to an allocated block.  Also pull the canon name
set into a separate function.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: DJ Delorie <dj@redhat.com>
(cherry picked from commit d01411f6)