Make Killing Floor 2 gamemode configurable

lgsm/config-default/config-lgsm/kf2server/_default.cfg

@@ -12,10 +12,11 @@
 ip="0.0.0.0"
 queryport="27015"
 defaultmap="KF-BioticsLab"
+gamemode="KFGameContent.KFGameInfo_VersusSurvival"
 
 ## Server Start Command | https://github.com/GameServerManagers/LinuxGSM/wiki/Start-Parameters#additional-parameters
 fn_parms(){
-parms="\"${defaultmap}?Game=KFGameContent.KFGameInfo_VersusSurvival?ConfigSubDir=${servicename} -QueryPort=${queryport}\""
+parms="\"${defaultmap}?Game=${gamemode}?ConfigSubDir=${servicename} -QueryPort=${queryport}\""
 }
 
 #### LinuxGSM Settings ####