nfsd: fix v4 reply caching

Very embarassing: 1091006c5e "nfsd: turn
on reply cache for NFSv4" missed a line, effectively leaving the reply
cache off in the v4 case.  I thought I'd tested that, but I guess not.

This time, wrote a pynfs test to confirm it works.

Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfssvc.c

@@ -640,7 +640,7 @@ nfsd_dispatch(struct svc_rqst *rqstp, __be32 *statp)
 	}
 
 	/* Store reply in cache. */
-	nfsd_cache_update(rqstp, proc->pc_cachetype, statp + 1);
+	nfsd_cache_update(rqstp, rqstp->rq_cachetype, statp + 1);
 	return 1;
 }