Use a banmask for multiplayer matches that have lobby-authentication enabled.
This prevents a lobby player banned by the host from rejoining after getting a new IP address and changing the rating part of the nickname, refs #5320, #3241 / rP17217, #3549 / rP21520 / D897.

Differential Revision: https://code.wildfiregames.com/D1655
Reproduced By: Hannibal_Barca