Improve source_info commenting and fix neutrino slow link

neutrinordp/xrdp-neutrinordp.h

@@ -61,6 +61,8 @@ struct pointer_item
 
 #define CURRENT_MOD_VER 4
 
+struct source_info;
+
 struct mod
 {
     int size; /* size of this struct */
@@ -183,7 +185,7 @@ struct mod
     tintptr handle; /* pointer to self as long */
     tintptr wm;
     tintptr painter;
-    tintptr si;
+    struct source_info *si;
 
     /* mod data */
     int sck;