NFSD: Short-circuit fh_verify tracepoints for LOCALIO

NFSD: Short-circuit fh_verify tracepoints for LOCALIO

LOCALIO will be able to call fh_verify() with a NULL rqstp. In this
case, the existing trace points need to be skipped because they
want to dereference the address fields in the passed-in rqstp.

Temporarily make these trace points conditional to avoid a seg
fault in this case. Putting the "rqstp != NULL" check in the trace
points themselves makes the check more efficient.

Signed-off-by: Chuck Lever <[email protected]>
Signed-off-by: Mike Snitzer <[email protected]>
Acked-by: Jeff Layton <[email protected]>
Reviewed-by: NeilBrown <[email protected]>
Signed-off-by: Anna Schumaker <[email protected]>