tipc: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

This patch fixes the following warnings:

net/tipc/link.c:1125:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
net/tipc/socket.c:736:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
net/tipc/socket.c:2418:7: warning: this statement may fall through [-Wimplicit-fallthrough=]

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enabling
-Wimplicit-fallthrough.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/link.c

@@ -1126,7 +1126,7 @@ static bool tipc_data_input(struct tipc_link *l, struct sk_buff *skb,
 			skb_queue_tail(mc_inputq, skb);
 			return true;
 		}
-		/* else: fall through */
+		/* fall through */
 	case CONN_MANAGER:
 		skb_queue_tail(inputq, skb);
 		return true;