liquidio: mark expected switch fall-through

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

Addresses-Coverity-ID: 143135 ("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/cavium/liquidio/lio_main.c

@@ -2209,6 +2209,7 @@ static int liquidio_ioctl(struct net_device *netdev, struct ifreq *ifr, int cmd)
 	case SIOCSHWTSTAMP:
 		if (lio->oct_dev->ptp_enable)
 			return hwtstamp_ioctl(netdev, ifr);
+		/* fall through */
 	default:
 		return -EOPNOTSUPP;
 	}