Implement the proxy and firewall ports section of Moat.jsm::_fixupSettings()
We need to actually implement setting firewall and proxy settings if received from rdsys as part of a censorship circumvention request. The first pass did not require this feature since rdsys doesn't currently have any censorship-circumvention settings requiring use of a proxy or firewall allow list, but it's best to have this feature ready to go for anti-censorship to use in the event it becomes useful in the future.