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 so it's never empty. Signed-off-by: Sieng Piaw Liew <liew.s.piaw@gmail.com>