decnet: af_decnet: mark expected switch fall-throughs

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/decnet/af_decnet.c

@@ -630,10 +630,12 @@ static void dn_destroy_sock(struct sock *sk)
 		goto disc_reject;
 	case DN_RUN:
 		scp->state = DN_DI;
+		/* fall through */
 	case DN_DI:
 	case DN_DR:
 disc_reject:
 		dn_nsp_send_disc(sk, NSP_DISCINIT, 0, sk->sk_allocation);
+		/* fall through */
 	case DN_NC:
 	case DN_NR:
 	case DN_RJ:
@@ -647,6 +649,7 @@ disc_reject:
 		break;
 	default:
 		printk(KERN_DEBUG "DECnet: dn_destroy_sock passed socket in invalid state\n");
+		/* fall through */
 	case DN_O:
 		dn_stop_slow_timer(sk);