vyos.ifconfig: T2104: support adding and removing VLANs in one call.

VLANIf('eth0.10').remove() will create and remove the VLAN in one command.
Thus one can ensure when calling remove() on a VLAN it will always
succeed.

(cherry picked from commit 7700da10b8d1d1b3d0db914ab48aebf8ff536da1)