[VLAN]: Make the vlan_name_type per-net.

This includes moving one on the struct vlan_net and
s/vlan_name_type/vn->name_type/ over the code.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>