statd: Support IPv6 is caller_is_localhost()

statd: Support IPv6 is caller_is_localhost()

For the time being, statd is not going to support receiving SM_MON
calls from the local lockd via IPv6.

However, the upcalls (SM_MON, etc.) from the local lockd arrive on the
same socket that receives calls from remote peers.  Thus
caller_is_localhost() at least has to be smart enough to notice that
the caller is not AF_INET, and to display non-AF_INET addresses
appropriately.

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