netvsc: make sure and unregister datapath

netvsc: make sure and unregister datapath

Go back to switching datapath directly in the notifier callback.
Otherwise datapath might not get switched on unregister.

No need for calling the NOTIFY_PEERS notifier since that is only for
a gratitious ARP/ND packet; but that is not required with Hyper-V
because both VF and synthetic NIC have the same MAC address.

Reported-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Fixes: 02e633075a17 ("netvsc: transparent VF management")
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>