[VLAN]: Create proc entries in the proper net.

The proc_vlan_dir and proc_vlan_conf migrate on the struct
vlan_net and their creation uses the struct net.

The devices' entries use the corresponding device's net.

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