statd: statd fails to monitor if no reverse mapping of mon_name exists

statd: statd fails to monitor if no reverse mapping of mon_name exists

Commit 8ce130c4 switched in the new statd_canonical_name() function
that constructs a "unique" name statd can use to uniquely identify a
monitor record.

The legacy statd would monitor a client that sent an IP address with
no reverse map as its caller_name.  To remain bug-for-bug compatible,
allow this case in the new statd.

This shouldn't be a problem: statd_canonical_name() needs to create
a unique name for the monitored host so it can keep track of monitor
requests from the same remote.  The IP address itself should work as
well as the host's canonical name, in case there is no reverse
mapping.

We still enforce the requirement that a mon_name that is a DNS name
must have a forward map to an IP address.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>