s390/qeth: reset NAPI context during queue init

init_qdio_queues() resets the Input Queue's overall QDIO state, and
positions the buffer cursor back to 0. So this is the obvious place to
also reset the queue's NAPI context (in contrast to doing it rather
randomly in the middle of the big set_online() path).
No functional change.

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