hv_netvsc: Fix net device attach on older Windows hosts

On older windows hosts the net_device instance is returned to
the caller of rndis_filter_device_add() without having the presence
bit set first. This would cause any subsequent calls to network device
operations (e.g. MTU change, channel change) to fail after the device
is detached once, returning -ENODEV.

Instead of returning the device instabce, we take the exit path where
we call netif_device_attach()

Fixes: 7b2ee50c ("hv_netvsc: common detach logic")
Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
Reviewed-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>