virtio-net: Refactor napi_disable paths

Create virtnet_napi_disable helper and refactor virtnet_napi_tx_disable
to take a struct send_queue.

Signed-off-by: Joe Damato <jdamato@fastly.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Link: https://patch.msgid.link/20250307011215.266806-3-jdamato@fastly.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>