MFC: Second part of Amazon ENA driver fixes and improvements

Now, the driver functionality is aligned with the latest version in HEAD.

r343074 Suppress excessive error prints in ENA TX hotpath
r336099 Add PNP info to PCI attachment of ena driver
r333456 Do not pass header length to the ENA controller
r333453 Apply fixes in ena-com
r333450 Upgrade ENA version to v0.8.1
r325593 Fix setting AENQ group in ENA driver
r325592 Allow usage of more RX descriptors than 1 in ENA driver
r325591 Read max MTU from the ENA device
r325590 Fix calculating io queues number in ENA driver
r325589 Rework printouts and logging level in ENA driver
r325587 Fix comparing L3 type with L4 enum on RX hash in ENA driver
r325586 Fix compilation warnings when building ENA driver with gcc compiler
r325585 Fix checking if the DF flag was set in ENA driver
r325584 Cleanup of the ENA driver header file
r325583 Allow partial MSI-x allocation in ENA driver
r325582 Remove deprecated and unused counters in ENA driver
r325581 Cover ENA driver code with branch predictioning statements

Sponsored by: Amazon, Inc.