opnsense-revert: Ability to force net family to connect with

[samip5]

Currently, if your IPv6 is currently borked, and you try to revert let's say dhcp6c, that would fix said issue, you're not able to revert at all due to it trying to access it via IPv6 and not failing back to v4.

[fichtner]

More or less same as #90

throwing code at it seems futile enough. If you can’t configure basic connectivity from the box all fetch tools will fail.

[samip5]

It's not futile, as one would expect tools to fallback which is not the case here.

It was trying to use a ULA gateway that I hadn't myself configured to get out with a public IPv6 address that I had configured for a VLAN.