eth: fbnic: add basic rtnl stats

Count packets, bytes and drop on the datapath, and report
to the user. Since queues are completely freed when the
device is down - accumulate the stats in the main netdev struct.
This means that per-queue stats will only report values since
last reset (per qstat recommendation).

Reviewed-by: Joe Damato <jdamato@fastly.com>
Link: https://patch.msgid.link/20240810054322.2766421-2-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>