Allow disabling server IP blocking

[dktapps]

When used in simple proxy systems, RakLib will see all packets coming from the same IP, which will cause IP banning to be triggered because of too many packets. It's also problematic if one session sends a bad packet, triggering IP banning which causes all players to be blocked for 5 seconds.

RakLib is not designed for use behind a proxy, and it really shouldn't be used that way. However, we can make the usage of RakLib in this scenario slightly less obnoxious for existing users by allowing the IP banning to be disabled.