napi_build_skb() reuses NAPI skbuff_head cache in order to save some
cycles on freeing/allocating skbuff_heads on every new Rx or completed
Tx.
Use napi_consume_skb() to feed the cache with skbuff_heads of completed
Tx. The budget parameter is added to indicate NAPI context, as a value
of zero can be passed in the case of netpoll.
NAT performance results on BT Home Hub 5A (kernel 5.15.45, mtu 1500):
Fast path (Software Flow Offload):
Up Down
Before 702.4 719.3
After 707.3 739.9
Slow path:
Up Down
Before 91.8 184.1
After 92.0 185.7
Signed-off-by: Aleksander Jan Bajkowski <olek2@xxxxx>