ice: Fix undersized tx_flags variable

As not all ICE_TX_FLAGS_* fit in current 16-bit limited
tx_flags field that was introduced in the Fixes commit,
VLAN-related information would be discarded completely.
As such, creating a vlan and trying to run ping through
would result in no traffic passing.

Fix that by refactoring tx_flags variable into flags only and
a separate variable that holds VLAN ID. As there is some space left,
type variable can fit between those two. Pahole reports no size
change to ice_tx_buf struct.

Fixes: aa1d3faf

 ("ice: Robustify cleaning/completing XDP Tx buffers")
Signed-off-by: Jan Sokolowski <jan.sokolowski@intel.com>
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>