i40e: mark expected switch fall-through

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

This patch fixes the following warning:

drivers/net/ethernet/intel/i40e/i40e_xsk.c: In function ‘i40e_run_xdp_zc’:
drivers/net/ethernet/intel/i40e/i40e_xsk.c:209:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
bpf_warn_invalid_xdp_action(act);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/intel/i40e/i40e_xsk.c:210:2: note: here
case XDP_ABORTED:
^~~~

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

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

---
 drivers/net/ethernet/intel/i40e/i40e_xsk.c | 1 +
 1 file changed, 1 insertion(+)

index e190a2c2b9ff..a02776cf1656 100644
@@ -207,6 +207,7 @@ static int i40e_run_xdp_zc(struct i40e_ring *rx_ring, struct xdp_buff *xdp)
 		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 */

2.20.1