NetPlay: Move NetSettings initialization to backend

It doesn't really belong in frontend code, and this change will make it
easier to eventually support NetPlay on other UI frameworks.

Source/Core/Core/NetPlayServer.h

@@ -50,8 +50,6 @@ public:
   bool AbortMD5();
   void SendChatMessage(const std::string& msg);
 
-  void SetNetSettings(const NetSettings& settings);
-
   bool DoAllPlayersHaveIPLDump() const;
   bool StartGame();
   bool RequestStartGame();
@@ -117,6 +115,7 @@ private:
     std::string title;
   };
 
+  bool SetupNetSettings();
   bool SyncSaveData();
   bool SyncCodes();
   void CheckSyncAndStartGame();