The guard in the b2.py patch block skipped setting get_restic_config when
something caused B2RcloneRemote.__dict__ to already contain it at import
time (e.g. a TrueNAS version that adds a NotImplementedError stub). Remove
the guard and always assign, which is safe: the native-support kill switch
already prevents patching when TrueNAS ships a real implementation.
Also update the native-support check to distinguish a stub (source contains
NotImplementedError) from a working implementation, so a stub does not
trigger the kill switch and block all future patching.