fix migration

[chrisguida]

The migration was messed up in two ways:

• technically v2transport doesn't exist yet and that will screw up trying to upgrade and downgrade with normal bitcoin core (switching back and forth between knots and core will probably always be awkward until support for two different packages with the same name is supported upstream)
• datacarrier, datacarriersize, and permitbaremultisig weren't being initialized, resulting in this message upon installation:

This PR fixes both issues.

[Retropex]

rebased and fixed in this commit d1c38f444f58340e6c7e48029e552d0644cc001e Thanks Chris!