hv_netvsc: fix locking during VF setup

The dev_uc/mc_sync calls need to have the device address list
locked. This was spotted by running with lockdep enabled.

Fixes: bee9d41b ("hv_netvsc: propagate rx filters to VF")
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>