i40e_txrx: mark expected switch fall-through

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

Addresses-Coverity-ID: 114791 ("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/intel/i40e/i40e_txrx.c

@@ -2253,9 +2253,10 @@ static struct sk_buff *i40e_run_xdp(struct i40e_ring *rx_ring,
 		break;
 	default:
 		bpf_warn_invalid_xdp_action(act);
+		/* fall through */
 	case XDP_ABORTED:
 		trace_xdp_exception(rx_ring->netdev, xdp_prog, act);
-		/* fallthrough -- handle aborts by dropping packet */
+		/* fall through -- handle aborts by dropping packet */
 	case XDP_DROP:
 		result = I40E_XDP_CONSUMED;
 		break;