NFS: don't negotiate when user specifies sec flavor

We were always attempting sec flavor negotiation, even if the user
told us a specific sec flavor to use.  If that sec flavor fails,
we should return an error rather than continuing with sec flavor
negotiation.

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/super.c

@@ -1004,6 +1004,7 @@ static int nfs_parse_security_flavors(char *value,
 		return 0;
 	}
 
+	mnt->flags |= NFS_MOUNT_SECFLAVOUR;
 	mnt->auth_flavor_len = 1;
 	return 1;
 }