veth: Avoid drop packets when xdp_redirect performs

In the current processing logic, when xdp_redirect occurs, it transmits
the xdp frame based on napi.

If napi of the peer veth is not ready, the veth will drop the packets.
This doesn't meet our expectations.

In this context, we enable napi of the peer veth automatically when the
veth loads the xdp. Then if the veth unloads the xdp, we need to
correctly judge whether to disable napi of the peer veth, because the peer
veth may have loaded xdp, or even the user has enabled GRO.

Signed-off-by: Heng Qi <henqqi@linux.alibaba.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>