mlxbf_gige: add support to display pause frame counters

mlxbf_gige: add support to display pause frame counters

This patch updates the mlxbf_gige driver to support the
"get_pause_stats()" callback, which enables display of
pause frame counters via "ethtool -I -a oob_net0".

The pause frame counters are only enabled if the "counters_en"
bit is asserted in the LLU general config register. The driver
will only report stats, and thus overwrite the default stats
state of ETHTOOL_STAT_NOT_SET, if "counters_en" is asserted.

Reviewed-by: Asmaa Mnebhi <asmaa@nvidia.com>
Signed-off-by: David Thompson <davthompson@nvidia.com>
Link: https://lore.kernel.org/r/20240305212137.3525-1-davthompson@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>