net: qualcomm: rmnet: Allow only one rmnet dev per muxid per real dev

Upon de-multiplexing data from one real dev, the packets can be sent
to an unique rmnet device for a given mux id.
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/qualcomm/rmnet/rmnet_vnd.c

@@ -185,6 +185,9 @@ int rmnet_vnd_newlink(u8 id, struct net_device *rmnet_dev,
 	if (ep->egress_dev)
 		return -EINVAL;
 
+	if (rmnet_get_endpoint(port, id))
+		return -EBUSY;
+
 	rc = register_netdevice(rmnet_dev);
 	if (!rc) {
 		ep->egress_dev = rmnet_dev;