s390/qeth: move NAPI poll routine to core

Identical code, we just need to call a layer-specific hook
to process any received buffer.

qeth_buffer_reclaim_work() is shuffled around to avoid a
forward declaration for qeth_queue_input_buffer().

Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Acked-by: Ursula Braun <ubraun@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>