multiplayer: the session imposes the settings that decide the physics

server_hello.config had been a TODO carrying a zero, and every peer ran with
whatever its own eu07.ini happened to say - including a vehicle physics thread
count, which makes the order vehicles are stepped in depend on how threads get
scheduled.

- the handshake now carries a bitfield of the settings that change how the
  physics comes out (full physics, realistic control) and a joining peer takes
  them on, saying in the log what changed
- a multiplayer session runs the vehicle physics on one thread on every peer,
  host included

Settings that only affect what a player sees or how comfortable the controls
feel stay with the player; only what alters the outcome belongs in here.

network/network.cpp

@@ -168,7 +168,7 @@ void network::server::handle_message(std::shared_ptr<connection> conn, const mes
 		server_hello reply;
 		reply.seed = Global.random_seed;
 		reply.timestamp = Global.starting_timestamp;
-        reply.config = 0; // TODO: pass bitfield with state of relevant setting switches
+        reply.config = pack_session_config();
         reply.scenario = Global.SceneryFile;
 		reply.app_version = Global.asVersion;
 		reply.session_token = cmd.session_token;
@@ -433,7 +433,7 @@ void network::client::handle_message(std::shared_ptr<connection> conn, const mes
 			Global.random_seed = cmd.seed;
 			Global.random_engine.seed(Global.random_seed);
 			Global.starting_timestamp = cmd.timestamp;
-            // TODO: configure simulation settings according to received cmd.config
+            apply_session_config(cmd.config);
             Global.SceneryFile = cmd.scenario;
 			Global.ready_to_load = true;