Add debugfs support for vlan configuraion. create a single file
"vlan_config" for it, and query it by command "cat vlan_config",
return the result to userspace.

The new display style is below:
$ cat vlan_config
I_PORT_VLAN_FILTER: on
E_PORT_VLAN_FILTER: off
FUNC_ID  I_VF_VLAN_FILTER  E_VF_VLAN_FILTER  PORT_VLAN_FILTER_BYPASS
pf       off               on                off
vf0      off               on                off
FUNC_ID  PVID    ACCEPT_TAG1  ACCEPT_TAG2  ACCEPT_UNTAG1  ACCEPT_UNTAG2
pf       0       on           on           on             on
vf0      0       on           on           on             on
Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>