net/ena: convert to new Tx offloads API

Ethdev Tx offloads API has changed since:

commit cba7f53b717d ("ethdev: introduce Tx queue offloads API")

This commit support the new Tx offloads API. Queue configuration
is stored in ena_ring.offloads. During preparing mbufs for tx, offloads are
allowed only if appropriate flags in this field are set.

Signed-off-by: Rafal Kozik <rk@semihalf.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Michal Krawczyk <mk@semihalf.com>