[NETSHELL] Optionally use the system's CLSID_ConnectionManager

Use a central compile option like we do in the rest of the shell so that when testing in windows we can switch using the one in the current dll or the one registered in the system.
Note that not only CLSID_ConnectionManager isn't implemented in netshell, it can't even be instantiated as CLSCTX_INPROC_SERVER because it is implemented by the netman service

dll/shellext/netshell/connectmanager.cpp

@@ -559,5 +559,9 @@ HRESULT CNetConnectionManager::Initialize()
 
 HRESULT WINAPI CNetConnectionManager_CreateInstance(REFIID riid, LPVOID * ppv)
 {
+#if USE_CUSTOM_CONMGR
     return ShellObjectCreatorInit<CNetConnectionManager>(riid, ppv);
+#else
+    return CoCreateInstance(CLSID_ConnectionManager, NULL, CLSCTX_ALL, riid, ppv);
+#endif
 }

dll/shellext/netshell/precomp.h

@@ -49,6 +49,8 @@ WINE_DEFAULT_DEBUG_CHANNEL(shell);
 #define NCF_FILTER                      0x400
 #define NCF_NDIS_PROTOCOL               0x4000
 
+#define USE_CUSTOM_CONMGR 1
+
 /* globals */
 extern HINSTANCE netshell_hInstance;