Do not pass header length to the ENA controller

Header length is optional hint for the ENA device. Because It is not
guaranteed that every packet header will be in the first mbuf
segment, it is better to skip passing any information. If the header
length will be indicating invalid value (different than 0), then the
packet will be dropped.

This kind situation can appear, when the UDP packet will be fragmented
by the stack in the ip_fragment() function.

Submitted by: Michal Krawczyk <mk@semihalf.com>
Reported by: Krishna Yenduri <kyenduri@brkt.com>
Obtained from: Semihalf
Sponsored by: Amazon, Inc.