mlxbf_gige: add support for pause frame counters

[David Thompson]

SRU Justification:

[Impact]

The BlueField-2 and BlueField-3 silicon designs include a
provision for reporting pause frame counters, but the driver
(mlxbf_gige) does not have software support yet.

[Fix]

The fix is to update the mlxbf_gige driver to support the
"get_pause_stats()" callback, which enables display of
pause frame counters via "ethtool -I -a ooob_net0".
The support of this callback was added to Linux kernel 5.9.0

[Test Case]

* Reboot BF platform, and configure oob_net0 interface
* Issue command "ethtool -I -a oob_net0" to display pause frame counters
* Send in multiple streams of traffic to oob_net0 interface, e.g. from
  two or three simultaneous SCP operations
* Re-issue "ethtool -I -a oob_net0" and note difference in output

[Regression Potential]

The changed logic extends the ethtool support, so low risk for any problem.

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is awaiting verification that the linux-bluefield/5.15.0-1039.41 kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-jammy-linux-bluefield' to 'verification-done-jammy-linux-bluefield'. If the problem still exists, change the tag 'verification-needed-jammy-linux-bluefield' to 'verification-failed-jammy-linux-bluefield'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!