ena: Update the license dating to 2023

Some of the files are using outdated linceses.
Update the license to be 2023.

Approved by: cperciva (mentor)
MFC after: 2 weeks
Sponsored by: Amazon, Inc.

sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

ena: Fix styling issues

Align code style with FreeBSD style(9) guidelines.

Obtained from: Semihalf
MFC after: 2 weeks
Sponsored by: Amazon, Inc.

ena: properly handle IPv6 L4 checksum offload

ena_tx_csum function did not check if IPv6 checksum offload was
requested it only checked checksum offloading flags for IPv4 packets.
Because of that, when encountering CSUM_IP6_* flags, the function simply
returned without actually setting checksum offloading in ena_ctx.
Check CUSM_IP6_* flags to enable IPv6 checksum offload.

Additionally, only IPv4 header was being parsed regardless of EtherType
field, because of that, value of L4 protocol read when actually trying
to send IPv6 packets was wrong. Use ip6_lasthdr function to get length
of all IPv6 headers and payload protocol.

Set the DF flag to 1 in order to allow the device to offload the IPv6
checksum calculation and achieve optimal performance.

Add CSUM6_OFFLOAD and CSUM_OFFLOAD definitions into ena_datapath.h.

Submitted by: Dawid Gorecki <dgr@semihalf.com>
Obtained from: Semihalf
MFC after: 2 weeks
Sponsored by: Amazon, Inc.

Add SPDX license tag to the ENA driver files

Refering to guide: https://wiki.freebsd.org/SPDX the SPDX tag should not
replace the standard license text, however it should be added over the
standard license text to make the automation easier.

Because of that, the old license was kept, but the SPDX tag was added
on top of every ENA driver file.

Submited by: Michal Krawczyk <mk@semihalf.com>
Obtained from: Semihalf
Sponsored by: Amazon, Inc
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D27117

Update ENA driver version to v2.2.0

Driver version upgrade is connected with support for the new device
fetures, like Tx drops reporting or disabling meta caching.

Moreover, the driver configuration from the sysctl was reworked to
provide safer and better flow for configuring:
* number of IO queues (new feature),
* drbr size on Tx,
* Rx queue size.

Moreover, a lot of minor bug fixes and improvements were added.

Copyright date in the license of the modified files in this release was
updated to 2020.

Submitted by: Michal Krawczyk <mk@semihalf.com>
Obtained from: Semihalf
Sponsored by: Amazon, Inc.

Expose argument names for non static ENA driver functions

As functions which are declared in the header files are intended to be
the interface and are going to be used by other files, it's better to
include argument names in the definition, so the caller won't have to
check the .c file in order to check their meaning and order.

Submitted by: Michal Krawczyk <mk@semihalf.com>
Obtained from: Semihalf
Sponsored by: Amazon, Inc.

Split Rx/Tx from initialization code in ENA driver

Move Rx/Tx routines to separate file.
Some functions:
* ena_restore_device,
* ena_destroy_device,
* ena_up,
* ena_down,
* ena_refill_rx_bufs
could be reused in upcoming netmap code in the driver. To make it
possible, they were moved to ena.h header.

Differential Revision: https://reviews.freebsd.org/D21933
Submitted by: Rafal Kozik <rk@semihalf.com>
Obtained from: Semihalf
Sponsored by: Amazon, Inc.