vlan: rework VLAN interface creation/deletion
First make it build on libnl1/2. Second, the VLAN virtual interface name might not always be given in the NMConnection (if the master is a UUID and thus the name is determined automatically) so just take the interface name instead. And make sure we verify it's a VLAN interface before deleting it. Lastly, construct the VLAN interface name if it's not given in the NMConnection. This means we need to know the master interface name when creating the connection, which we always will since you can't create the VLAN interface without it's master being present. That also means we need to return the name to the caller so it can be used to create the NMDevice for the VLAN interface after we've created it in the kernel.
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