statd: Introduce statd version of matchhostname()

statd: Introduce statd version of matchhostname()

For the near future, statd will support IPv6 but exportfs will not.
Thus statd will need a version of matchhostname() that can deal
properly with IPv6 remotes.  To reduce the risk of breaking exportfs,
introduce a separate version of matchhostname() for statd to use while
exportfs continues to use the existing AF_INET-only implementation.

Note that statd will never send matchhostname() a hostname string
containing export wildcards, so is_hostame() is not needed in the
statd version of matchhostname().  This saves some computational
expense when comparing hostnames.

A separate statd-specific implementation of matchhostname() allows
some flexibility in the long term, as well.  We might want to enrich
the matching heuristics of our SM_NOTIFY, for example, or replace
them entirely with a heuristic that is not dependent upon DNS.

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