lnc: add timeout to the inital grpc connection with Mailbox

Make sure that we do not hold forever if we are not able to dial with
the maiblox service.

This could happen in cases where a passphrase is being reused
and the secret key has already been negotiated for example.

lnc/lnc.go

@@ -281,8 +281,11 @@ func (n *NodeConn) newConn(session *Session, opts ...grpc.DialOption) (*conn,
 	}
 	dialOpts = append(dialOpts, opts...)
 
+	ctxt, cancelT := context.WithTimeout(ctxc, DefaultConnectionTimetout)
+	defer cancelT()
+
 	grpcClient, err := grpc.DialContext(
-		ctxc, session.MailboxAddr, dialOpts...,
+		ctxt, session.MailboxAddr, dialOpts...,
 	)
 	if err != nil {
 		cancel()