net/ena: fix meta descriptor DF flag setup

net/ena: fix meta descriptor DF flag setup

Whenever Tx checksum offload is being used, the meta descriptor content
is taken into consideration. Setting DF field properly in the meta
descriptor may have huge impact on the performance both for the IPv4 and
IPv6 packets.

The requirements for the df field are as below:
* No offload used - value doesn't matter
* IPv4 - 0 or 1, depending on the DF flag in the IPv4 header
* IPv6 - 1

Setting DF to 0 causes the packet to enter the slow-path in the HW and
as a result can noticeable impact the performance.

Moreover, as 'true' may not always be mapped to 1 depending on it's
definition for the given platform/compiler, for safety DF field is being
set explicitly to 1.

Fixes: 1173fca25af9 ("ena: add polling-mode driver")
Cc: stable@dpdk.org
Signed-off-by: Michal Krawczyk <mk@semihalf.com>
Reviewed-by: Dawid Gorecki <dgr@semihalf.com>
Reviewed-by: Shai Brandes <shaibran@amazon.com>