net: decnet: dn_nsp_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: NGustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/decnet/dn_nsp_in.c

@@ -491,6 +491,7 @@ static void dn_nsp_disc_conf(struct sock *sk, struct sk_buff *skb)
 		break;
 	case DN_RUN:
 		sk->sk_shutdown |= SHUTDOWN_MASK;
+		/* fall through */
 	case DN_CC:
 		scp->state = DN_CN;
 	}