hv_netvsc: simplify callback event code

hv_netvsc: simplify callback event code

The callback handler for netlink events can be simplified:
 * Consolidate check for netlink callback events about this driver itself.
 * Ignore non-Ethernet devices.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>