hv_netvsc: Sync offloading features to VF NIC

VF NIC may go down then come up during host servicing events. This
causes the VF NIC offloading feature settings to roll back to the
defaults. This patch can synchronize features from synthetic NIC to
the VF NIC during ndo_set_features (ethtool -K),
and netvsc_register_vf when VF comes back after host events.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Mark Bloch <markb@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>