cxgb4/l2t: Mark expected switch fall-through

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

Addresses-Coverity-ID: 114910 ("Missing break in switch")
Signed-off-by: NGustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb4/l2t.c

@@ -231,6 +231,7 @@ int cxgb4_l2t_send(struct net_device *dev, struct sk_buff *skb,
 		if (e->state == L2T_STATE_STALE)
 			e->state = L2T_STATE_VALID;
 		spin_unlock_bh(&e->lock);
+		/* fall through */
 	case L2T_STATE_VALID:     /* fast-path, send the packet on */
 		return t4_ofld_send(adap, skb);
 	case L2T_STATE_RESOLVING: