ixgbe: Resolve warnings for -Wimplicit-fallthrough

This patch adds/changes fall through comments to address new warnings
produced by gcc 7.

Fixed formatting on a couple of comments in the function.

Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
index cced74d..9113e80 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
@@ -2668,6 +2668,7 @@ static int ixgbe_flowspec_to_flow_type(struct ethtool_rx_flow_spec *fsp,
 				*flow_type = IXGBE_ATR_FLOW_TYPE_IPV4;
 				break;
 			}
+			/* fall through */
 		default:
 			return 0;
 		}