net-next: ax88796: add interrupt status callback to platform data

To be able to tell the ax88796 driver whether it is sensible to enter
the 8390 interrupt handler, an "is this interrupt caused by the 88796"
callback has been added to the ax_plat_data structure (with NULL being
compatible to the previous behaviour).

Signed-off-by: Michael Karcher <kernel@mkarcher.dialup.fu-berlin.de>
Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>