added mode L3_SUB_VLAN as tagged

[barriejc]

Working with Jeremy White at the NANOG88 hackathon June 11, 2023, we identified a few issues with adapters/nautobot_api/models.py in the network-importer instance I had installed a few months before on February 9. The Vlan tag creation issue was solved with slugify(self.name) but it seems to have been fixed in develop on Feb. 2 with this:

tag = self.diffsync.nautobot.extras.tags.create(
                name=f"device={self.name}", slug=f"device__{''.join(c if c.isalnum() else '_' for c in self.name)}"
            )

As a result, I'm only including the L3_SUB_VLAN tagged mode fix.

[chadell]

LGTM