eth: fbnic: Add pause stats support

eth: fbnic: Add pause stats support

Add support to read pause stats for fbnic. Unlike FEC and PCS stats,
pause stats won't wrap, do not fetch them under the service task. Since,
they are exclusively accessed via the ethtool API, don't include them in
fbnic_get_hw_stats().

]# ethtool -I -a eth0
Pause parameters for eth0:
Autonegotiate:	on
RX:		off
TX:		off
Statistics:
  tx_pause_frames: 0
  rx_pause_frames: 0

Signed-off-by: Mohsin Bashir <mohsin.bashr@gmail.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20250825200206.2357713-7-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>