[MBsysPy][MbsDirdyn] Add the number of buffer in the properties.

MBsysC/mbs_interface/MBsysPy/mbsyspy/mbs_dirdyn.py

@@ -877,6 +877,11 @@ class MbsDirdyn(object):
         """Access to `dt` attribute (read-only)."""
         return self.mbs_dirdyn_ptr.contents.dt
 
+    @property
+    def buffer_nb(self):
+        """Access to `bufferNb` attribute (read-only)."""
+        return self.mbs_dirdyn_ptr.contents.bufferNb
+
 
 class MbsResult(object):
     """