Better checks for Multiplayer API, prevent packet source spoofing.
Better checks for Multiplayer API, prevent packet source spoofing.

Fixes the following problems.

A malicious client was able to contact another peer faking its identity
(even looking like he was the server).

A malicious client was able to force other client disconnections by sending
bogus system packets to the server.

Max-Might/godot,Valentactive/godot,okamstudio/godot,DmitriySalnikov/godot,firefly2442/godot,ficoos/godot,ex/godot,zicklag/godot,Marqin/godot,vkbsb/godot,okamstudio/godot,josempans/godot,Paulloz/godot,RandomShaper/godot,vkbsb/godot,sanikoyes/godot,pkowal1982/godot,akien-mga/godot,Brickcaster/godot,jejung/godot,guilhermefelipecgs/godot,akien-mga/godot,honix/godot,DmitriySalnikov/godot,Zylann/godot,vnen/godot,Paulloz/godot,RebelliousX/Go_Dot,honix/godot,NateWardawg/godot,godotengine/godot,pkowal1982/godot,DmitriySalnikov/godot,Zylann/godot,ZuBsPaCe/godot,ex/godot,Faless/godot,sanikoyes/godot,Zylann/godot,zicklag/godot,ficoos/godot,Max-Might/godot,guilhermefelipecgs/godot,ficoos/godot,ZuBsPaCe/godot,RandomShaper/godot,guilhermefelipecgs/godot,zicklag/godot,okamstudio/godot,n-pigeon/godot,morrow1nd/godot,RebelliousX/Go_Dot,exabon/godot,sanikoyes/godot,MrMaidx/godot,ficoos/godot,NateWardawg/godot,tomreyn/godot,groud/godot,MrMaidx/godot,guilhermefelipecgs/godot,n-pigeon/godot,RandomShaper/godot,godotengine/godot,Faless/godot,BastiaanOlij/godot,tomreyn/godot,ageazrael/godot,vnen/godot,RebelliousX/Go_Dot,Max-Might/godot,MarianoGnu/godot,ZuBsPaCe/godot,Brickcaster/godot,Zylann/godot,morrow1nd/godot,honix/godot,Valentactive/godot,Faless/godot,RandomShaper/godot,tomreyn/godot,jejung/godot,Shockblast/godot,pkowal1982/godot,vkbsb/godot,Shockblast/godot,honix/godot,Faless/godot,NateWardawg/godot,exabon/godot,Zylann/godot,pkowal1982/godot,vnen/godot,josempans/godot,Shockblast/godot,mcanders/godot,sanikoyes/godot,MarianoGnu/godot,n-pigeon/godot,josempans/godot,exabon/godot,mcanders/godot,ZuBsPaCe/godot,pkowal1982/godot,Marqin/godot,firefly2442/godot,Shockblast/godot,BastiaanOlij/godot,sanikoyes/godot,ficoos/godot,vkbsb/godot,ex/godot,Shockblast/godot,Zylann/godot,BastiaanOlij/godot,tomreyn/godot,godotengine/godot,Marqin/godot,morrow1nd/godot,vkbsb/godot,Paulloz/godot,Valentactive/godot,vnen/godot,Valentactive/godot,DmitriySalnikov/godot,Shockblast/godot,MrMaidx/godot,firefly2442/godot,Faless/godot,zicklag/godot,n-pigeon/godot,Brickcaster/godot,firefly2442/godot,RandomShaper/godot,FateAce/godot,Shockblast/godot,vnen/godot,morrow1nd/godot,DmitriySalnikov/godot,BastiaanOlij/godot,sanikoyes/godot,NateWardawg/godot,ex/godot,NateWardawg/godot,okamstudio/godot,BastiaanOlij/godot,Max-Might/godot,MarianoGnu/godot,Paulloz/godot,BastiaanOlij/godot,ageazrael/godot,morrow1nd/godot,groud/godot,ZuBsPaCe/godot,ZuBsPaCe/godot,pkowal1982/godot,guilhermefelipecgs/godot,ageazrael/godot,ageazrael/godot,MarianoGnu/godot,guilhermefelipecgs/godot,vnen/godot,firefly2442/godot,n-pigeon/godot,NateWardawg/godot,josempans/godot,groud/godot,RandomShaper/godot,okamstudio/godot,FateAce/godot,FateAce/godot,Faless/godot,josempans/godot,NateWardawg/godot,Valentactive/godot,BastiaanOlij/godot,RandomShaper/godot,mcanders/godot,Brickcaster/godot,ex/godot,Paulloz/godot,zicklag/godot,mcanders/godot,okamstudio/godot,n-pigeon/godot,jejung/godot,Zylann/godot,Max-Might/godot,godotengine/godot,firefly2442/godot,groud/godot,groud/godot,ageazrael/godot,Valentactive/godot,akien-mga/godot,NateWardawg/godot,firefly2442/godot,exabon/godot,Brickcaster/godot,FateAce/godot,DmitriySalnikov/godot,vkbsb/godot,pkowal1982/godot,Max-Might/godot,godotengine/godot,Brickcaster/godot,MarianoGnu/godot,pkowal1982/godot,jejung/godot,Zylann/godot,RebelliousX/Go_Dot,MrMaidx/godot,ficoos/godot,vnen/godot,okamstudio/godot,okamstudio/godot,guilhermefelipecgs/godot,vkbsb/godot,Marqin/godot,BastiaanOlij/godot,MarianoGnu/godot,godotengine/godot,ex/godot,n-pigeon/godot,godotengine/godot,vkbsb/godot,groud/godot,Brickcaster/godot,honix/godot,Faless/godot,firefly2442/godot,MarianoGnu/godot,ex/godot,ageazrael/godot,akien-mga/godot,Valentactive/godot,jejung/godot,exabon/godot,zicklag/godot,akien-mga/godot,Shockblast/godot,mcanders/godot,josempans/godot,MarianoGnu/godot,akien-mga/godot,Marqin/godot,FateAce/godot,exabon/godot,josempans/godot,sanikoyes/godot,Paulloz/godot,NateWardawg/godot,josempans/godot,Valentactive/godot,tomreyn/godot,RebelliousX/Go_Dot,Marqin/godot,ZuBsPaCe/godot,jejung/godot,vnen/godot,guilhermefelipecgs/godot,okamstudio/godot,sanikoyes/godot,ageazrael/godot,Faless/godot,akien-mga/godot,FateAce/godot,RebelliousX/Go_Dot,mcanders/godot,ex/godot,ZuBsPaCe/godot,DmitriySalnikov/godot,honix/godot,okamstudio/godot,godotengine/godot,Paulloz/godot,akien-mga/godot,MrMaidx/godot,morrow1nd/godot,MrMaidx/godot