Fix frame id in diff_drive_controller (#521)

[tverbele]

Strips first "/" from namespace and only append once.

[destogl]

Thanks! The old code seems odd. Now, sure, if there were a specific reason to do that.

I agree, but the code looks strange/complicated in general. Can we write a test – to understand how this is used at all.

[bmagyar]

... or at least document how you can get the current setup to fail

correction
It was documented in #521

[bmagyar]

TBH the erase line could do with a comment to document it a bit but I think that the appending of namespaces is the result of a conflict resolution gone wrong @destogl , those lines are just plain dumb, we should merge this asap

[destogl]

Thanks!