addons: vlan: error out when vlan-raw-device config change on existing vlan

addons: vlan: error out when vlan-raw-device config change on existing vlan

kernel doesn't support vlan raw-device change on existing vlan, user needs to
manually ifdown/ifup the device

[13:45:06] root:~ # ifquery vlan42
auto vlan42
iface vlan42
      address 42.42.42.42/24
      vlan-id 42
      vlan-raw-device swp1

[13:45:07] root:~ # ifup -a
[13:45:09] root:~ # echo $?
0
[13:45:10] root:~ # ip link show vlan42
34: vlan42@swp1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default
    link/ether 90:e2:ba:2c:b1:96 brd ff:ff:ff:ff:ff:ff
[13:45:13] root:~ # nano /etc/network/interfaces
[13:45:19] root:~ # ifquery vlan42
auto vlan42
iface vlan42
      address 42.42.42.42/24
      vlan-id 42
      vlan-raw-device swp2

[13:45:25] root:~ # ifreload -a
error: vlan42: cannot change vlan-raw-device from swp1 to swp2: operation not supported. Please delete the device with 'ifdown vlan42' and recreate it to apply the change.
[13:45:27] root:~ # echo $?
1
[13:45:30] root:~ #

Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>