slic: remove a copy of the NAPI_POLL_WEIGHT define

Defining local versions of NAPI_POLL_WEIGHT with the same
values in the drivers just makes refactoring harder.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>