CasaOS Gateway vulnerable to incorrect identification of source IP addresses

CasaOS is an open-source Personal Cloud system. Due to a lack of IP address verification an unauthenticated attackers can execute arbitrary commands as `root` on CasaOS instances. The problem was addressed by improving the detection of client IP addresses in `391dd7f`. This patch is part of CasaOS 0.4.4. Users should upgrade to CasaOS 0.4.4. If they can't, they should temporarily restrict access to CasaOS to untrusted users, for instance by not exposing it publicly.