Use napi to reduce overhead on rx interrupts.

Driver used to interrupt kernel for every Rx packet, this could
affect both system and network performance. NAPI is a mechanism that
uses polling when processing huge amount of traffic, by doing this
the number of interrupts can be decreased.

Network performance can also benefit from this patch. Since TCP
connection is bidirectional and acks are required for every several
packets. These ack packets occupie the PCI bus bandwidth and could
lead to performance degradation.

When napi is used, GRO receive is enabled by default in the mac80211
stack. So mac80211 won't pass every RX TCP packets to the kernel TCP
network stack immediately. Instead an aggregated large length TCP packet
will be delivered.

This reduces the tx acks sent and gains rx performance. After the patch,
the Rx throughput increases about 25Mbps in 11ac.
Signed-off-by: Po-Hao Huang <phhuang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Tested-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210209070755.23019-4-pkshih@realtek.com