The netvsc_device structure should be accessed by rcu_dereference
in the send path.  Change arguments to netvsc_send() to make
this easier to do correctly.

Remove no longer needed hv_device_to_netvsc_device.
Signed-off-by: NStephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>