Private/conflicting ol_flags where used to enable UDP/TCP Tx
offloads. Use the common flags in PKT_TX_L4_MASK to support them.
When updating flags, also do some minor code rearranging for
slightly better performane.
Fixes: fefed3d1e62c ("enic: new driver") Signed-off-by: John Daley <johndale@cisco.com>