nfp: make use of napi_consume_skb()

Use napi_consume_skb() in nfp_net_tx_complete() to get bulk free.
Pass 0 as budget for ctrl queue completion since it runs out of
a tasklet.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>