hv_netvsc: set master device

The hyper-v transparent bonding should have used master_dev_link.
The netvsc device should look like a master bond device not
like the upper side of a tunnel.

This makes the semantics the same so that userspace applications
looking at network devices see the correct master relationshipship.

Fixes: 0c195567

 ("netvsc: transparent VF management")
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>