IB/hfi1: use new function dev_fetch_sw_netstats

Simplify the code by using new function dev_fetch_sw_netstats().

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/6cad1a04-f021-d94b-45fd-7cc7cf07367d@gmail.com


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