eth: fbnic: Fetch TX pause storm stats

eth: fbnic: Fetch TX pause storm stats

With pause storm protection in place, track the occurrence of pause
storm events. Since there is a one-to-one mapping between pause storm
interrupts and events, use the interrupt count to track this metric.

./ethtool -I -a eth0
Pause parameters for eth0:
Autonegotiate:	off
RX:		off
TX:		on
Statistics:
  tx_pause_frames: 759657
  rx_pause_frames: 0
  tx_pause_storm_events: 219

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Mohsin Bashir <mohsin.bashr@gmail.com>
Link: https://patch.msgid.link/20260302230149.1580195-5-mohsin.bashr@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>