Add check on network interface name's length

[DUFOUR Olivier]

When adding a VLAN on long network interfaces, Cloud-init will fail silently to add the sub-interfaces.

Deployed environment is :
* MAAS 3.3.4
* Server Dell R630 + Mellanox Connectx-5
* name of interfaces : enp130s0f0np0 / enp130s0f1np1
* add a VLAN like 100-4093

Cloud-Init will not display any error message but the VLAN interfaces will not be added after the deployment.
If trying to perform the operation manually, we are then greeted with the following error message.

```
ubuntu@R630:~$ sudo ip link add link enp130s0f0np0 name enp130s0f0np0.103 type vlan id 103
Error: argument "enp130s0f0np0.103" is wrong: "name" not a valid ifname
```

From Iproute2 and Kernel perspective, it is not possible to have interfaces with a name longer than 15 characters in total.

A quick workaround is simply to rename the network interface to something shorter.
Having a quick warning from MAAS would be nice to have to understand the origin of the issue.

[Christian Grabowski (cgrabowski)]

Can reproduce, moving to triaged.

[Adam Collard (adam-collard)]

Let's make MAAS not create names for interfaces that are > 15 characters long.

Cloud-init should reject the names if it's told to create interfaces that don't have valid names

[James Falcon (falcojr)]

The remote watcher automatically changed this bug to "New", which will cause problems with our triaging. Changing it back to manual. Please see https://github.com/canonical/cloud-init/issues/4743 for any updates on the cloud-init side

[Chad Smith (chad.smith)]

PR in flight https://github.com/canonical/cloud-init/pull/4774