net: netrom: nr_in: mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netrom/nr_in.c

@@ -125,7 +125,7 @@ static int nr_state2_machine(struct sock *sk, struct sk_buff *skb,
 
 	case NR_DISCREQ:
 		nr_write_internal(sk, NR_DISCACK);
-
+		/* fall through */
 	case NR_DISCACK:
 		nr_disconnect(sk, 0);
 		break;