[NETSHELL] Add missing license headers

Since one of the first files in the module (shfldr_netconnect.c) used the LGPL2.1+ license, all the other files have the same license

dll/shellext/netshell/netshell.cpp

@@ -1,3 +1,10 @@
+/*
+ * PROJECT:     ReactOS Shell
+ * LICENSE:     LGPL-2.1-or-later (https://spdx.org/licenses/LGPL-2.1-or-later)
+ * PURPOSE:     ReactOS Networking Configuration
+ * COPYRIGHT:   Copyright 2008 Johannes Anderwald (johannes.anderwald@reactos.org)
+ */
+
 #include "precomp.h"
 
 #include <olectl.h>