virtio_net: Add schedule check to napi_enable call

virtio_net: Add schedule check to napi_enable call

commit 3e9d08ec0a68f6faf718d5a7e050fe5ca0ba004f upstream.

Under harsh testing conditions, including low memory, the guest would
stop receiving packets. With this patch applied we no longer see any
problems in the driver while performing these tests for extended periods
of time.

Make sure napi is scheduled subsequent to each napi_enable.

[PG: in 34, virtqueue_disable_cb is vi->rvq->vq_ops->disable_cb]

Signed-off-by: Bruce Rogers <brogers@novell.com>
Signed-off-by: Olaf Kirch <okir@suse.de>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>