Fixes #3589: Interface VLAN filtering

[hSaria]

Fixes: #3589

• Perform validation on the tagged VLANs similar to that which is already performed on the untagged VLAN
• Removes the legacy choices filter that is no longer used because the API-based select widgets override the choices
• Limit the select filter to only global VLANs or VLANs in the same site as the device

Because there currently isn't a way to specify multiple values for the same parameter, I had to work around it.

[hSaria]

@jeremystretch FYI, this is currently waiting on your input regarding multiple values for the same field. The current implementation will override the field I've put in the additional_query_params of the widget.

I'm hoping there's a better way, but I can think of only two ways to do it:

• Key-based: use a different key which will map to the same field once the code in forms.js processes it (what I did, but perhaps in a better way than just prepending 1-)
• Value-based: Use some character to indicate multiple values in the field (e.g. add_additional_query_param('site_id', 'null,{}'.format(self.parent_obj.site.pk))) and have forms.js split on that character.

[hSaria]

I have removed the select widget filtering changes from this PR as they will be covered in a different PR for #3840.

This PR just adds validation for the tagged VLANs of an interface. It also cleans up the filtering that is no longer needed because of #3812.