Handle VLAN updates

[sajith]

With PR #120, we will add a way to assign VLAN to connection requests, but it is only an initial sketch. We're missing a design and implementation to handle updates.

This is related to this TODO item:

pce/src/sdx/pce/topology/temanager.py

Lines 94 to 99 in 1e19555

	# TODO: careful here when updating VLAN tags table -- what do
	# we do when an in use VLAN tag becomes invalid in the update?
	# self._update_vlan_tags_table_from_links(
	# domain_name=topology_data.get("id"),
	# port_list=self.topology_manager.port_list,
	# )

[italovalcy]

Some discussion needs to be done here to better define the use case and expected behavior:

What happens is that the OXP modifies the VLAN range available for SDX, and L2VPN services are already using the removed VLAN.

• Should we just ignore that change?
• Mark the VLAN as removed and allow existing L2VPN to exist, but not allow new L2VPN service be created with that VLAN? (after freeing up the existing one)?
• Remove the existing L2VPN and mark them with error status?

[YufengXin]

My opinion is to distinguish between management function and control function: this is a case of management function, which I think should be defined as out of scope for now.