[PATCH v2 0/2] virtio_net: fix race in RX VQ processing

Jason Wang reported a race in RX VQ processing:
virtqueue_enable_cb is called outside napi lock,
violating virtio serialization rules.
The race has been there from day 1, but it got especially nasty in 3.0
when commit a5c262c5fd83ece01bd649fb08416c501d4c59d7
"virtio_ring: support event idx feature"
added more dependency on vq state.

Please review, and consider for 3.11 and stable.

Changes from v1:
	- Added Jason's Tested-by tag
	- minor coding style fix