When vlan ctag filter is enabled, the loopback selftest fails because
loopback selftest does not support vlan.

This patch fixes it by disabling the vlan ctag filter when runnig
loopback selftest.
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>