Rename Interface form_factor to type

[jeremystretch]

Proposed Changes

Rename the form_factor field on the dcim.Interface model to type, and update forms and serializers accordingly.

Justification

"Form factor" is a misnomer given the field's purpose in conveying specific network technologies. For example, 100 Mbps and 1 Gbps Ethernet can both utilize the 8P8C copper form factor, but provide two different types of services and employ different wire protocols.

[lampwins]

@jeremystretch I think we should we allow a period of backward compatibility in the API. Say go ahead and change the model field but in the API continue to allow the use of form_factor for a period of time (I suggest until 2.7)? I foresee this being one of those nasty breaking changes for a lot of people and thus a reason to delay 2.6 adoption.

[jeremystretch]

Yeah, I've been asking myself whether it's honestly worth the hassle. I suppose we could migrate the field name, then add a getter/setter named form_factor with a deprecation warning to retain backward compatibility until v2.7.

[jeremystretch]

I've renamed form_factor to type but added a new form_factor field to replicate the functionality of type for backward compatibility. form_factor will be fully removed in NetBox v2.7.