Some more fixups for fwbank, this time on the frontend/rpcd side

• Rename one argument name in the dump() method in fwbank ("uri" -> "path"). While at it, remove any reference to remote http(s) url stuff, implying we only support upgrading from a file on the filesystem.
• Ensure the "auto_activate" argument in the upgrade() method is of the boolean type. (this already sort-of-worked, but now I think I resolved all the snags)
• Try really hard to output the list of banks by bank id when ubus call fwbank dump is invoked.