net: aquantia: extract timer cb into work job

Service timer callback fetches statistics from FW and that may cause
a long delay in error cases. We also now need to use fw mutex
to prevent concurrent access to FW, thus - extract that logic
from timer callback into the job in the separate work queue.

Signed-off-by: Nikita Danilov <ndanilov@aquantia.com>
Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>