netxen_nic: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a warning
by explicitly adding a goto statement instead of just letting the code
fall through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

drivers/net/ethernet/qlogic/netxen/netxen_nic_init.c

@@ -1685,6 +1685,7 @@ netxen_process_rcv_ring(struct nx_host_sds_ring *sds_ring, int max)
 			break;
 		case NETXEN_NIC_RESPONSE_DESC:
 			netxen_handle_fw_message(desc_cnt, consumer, sds_ring);
+			goto skip;
 		default:
 			goto skip;
 		}