main: create parent directories of NMSTATEDIR with permissions 755

In case, "$PREFIX/var/lib" does not exist, we want to create those
directories with permissions 755, not 700.

src/main-utils.h

@@ -27,6 +27,7 @@ void     nm_main_utils_ensure_root (void);
 
 void     nm_main_utils_setup_signals (GMainLoop *main_loop);
 
+void     nm_main_utils_ensure_statedir (void);
 void     nm_main_utils_ensure_rundir (void);
 
 gboolean nm_main_utils_write_pidfile (const char *pidfile);