propagate Required flag to Slot

OpenRA.Game/Network/Session.cs

@@ -64,6 +64,7 @@ namespace OpenRA.Network
 			public bool LockColor;
 			public bool LockTeam;
 			public bool LockSpawn;
+			public bool Required;
 		}
 
 		public class Global

OpenRA.Mods.RA/ServerTraits/LobbyCommands.cs

@@ -451,7 +451,8 @@ namespace OpenRA.Mods.RA.Server
 				LockRace = pr.LockRace,
 				LockColor = pr.LockColor,
 				LockTeam = pr.LockTeam,
-				LockSpawn = pr.LockSpawn
+				LockSpawn = pr.LockSpawn,
+				Required = pr.Required,
 			};
 		}