Update IP forwarding to ignore FML tokens (for now)

For Forge 1.8, a new \0FML\0 token is included in the handshake packet host field. Whilst from a Forge <-> Bungee standpoint, this is good in the long run (we can detect Forge/FML clients right from the off, allowing us to expose a reliable API for detecting modded 1.8+ clients), it plays havoc with IP forwarding on Spigot servers, as they expect a very specific format.

Until we can look at improving this situation (probably by creating an updated IP forwarding protocol on the server side), this removes the FML marker from the handshake whenever IP forwarding is on. If you have a FML 1.8 network, IP forwarding MUST be off.

With thanks to @geNAZt for finding the issue.