NLM: Shrink the IPv4-only version of nlm_cmp_addr()

Clean up/micro-optimatization:  Make the AF_INET-only version of
nlm_cmp_addr() smaller.  This matches the style of
nlm_privileged_requester(), and makes the AF_INET-only version of
nlm_cmp_addr() nearly the same size as it was before IPv6 support.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>