s390/qeth: enable napi_consume_skb() for pending TX buffers

Pending TX buffers are completed from the same NAPI code as normal
TX buffers. Pass the NAPI budget to qeth_tx_complete_buf() so that
the freeing of the completed skbs can be deferred.

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