vlan: partially enable SIOCSHWTSTAMP in container

Setting timestamp filter was explicitly disabled on vlan devices in
containers because it might affect other processes on the host. But it's
absolutely legit in case when real device is in the same namespace.

Fixes: 873017af

 ("vlan: disable SIOCSHWTSTAMP in container")
Signed-off-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Signed-off-by: David S. Miller <davem@davemloft.net>