SUNRPC: setup rpcbind clients if service requires it

New function ("svc_uses_rpcbind") will be used to detect, that new service will
send portmapper register calls. For such services we will create rpcbind
clients and remove all stale portmap registrations.
Also, svc_rpcb_cleanup() will be set as sv_shutdown callback for such services
in case of this field wasn't initialized earlier. This will allow to destroy
rpcbind clients when no other users of them left.

Note: Currently, any creating service will be detected as portmap user.
Probably, this is wrong. But now it depends on program versions "vs_hidden"
flag.
Signed-off-by: NStanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/svc.c

@@ -454,8 +454,15 @@ __svc_create(struct svc_program *prog, unsigned int bufsize, int npools,
 		spin_lock_init(&pool->sp_lock);
 	}
 
-	/* Remove any stale portmap registrations */
-	svc_unregister(serv);
+	if (svc_uses_rpcbind(serv)) {
+	       	if (svc_rpcb_setup(serv) < 0) {
+			kfree(serv->sv_pools);
+			kfree(serv);
+			return NULL;
+		}
+		if (!serv->sv_shutdown)
+			serv->sv_shutdown = svc_rpcb_cleanup;
+	}
 
 	return serv;
 }