Interface allows non existent VLAN to be tagged #120

It is possible to tag a VLAN or VLAN range on an interface without the VLAN actually existing. When you create the VLAN afterwards, it is not working and needs to be added again.

1. Tag a non existent VLAN on an interface, e.g.

interface PortChannel10
 switchport trunk allowed Vlan add 12
!

2. Create the VLAN afterwards (e.g. interface Vlan12)
3. Now the VLAN is not working, even though we tagged it:

sonic# show Vlan 12
Q: A - Access (Untagged), T - Tagged
NUM        Status      Q Ports            Autostate   Dynamic
12         Inactive                        Enable

4. Repeat step 1 and afterwards repeat step 3 to see it now working.

I think the KLISH CLI should throw an error when you try to tag a VLAN that is not yet created. This will avoid both the situation described above, and will clarify for users that VLANs need to be created first.

Edit: This might also effect the 'all' tagging option