server session CHANGE function to check whether a session is call home

Refs cesnet/netopeer2#398
diff --git a/src/session_server.h b/src/session_server.h
index 95dd12c..c3e584c 100644
--- a/src/session_server.h
+++ b/src/session_server.h
@@ -860,6 +860,15 @@
  */
 int nc_session_get_notif_status(const struct nc_session *session);
 
+/**
+ * @brief Learn whether a session was created using Call Home or not.
+ * Works only for server sessions.
+ *
+ * @param[in] session Session to get the information from.
+ * @return 0 if a standard session, non-zero if a Call Home session.
+ */
+int nc_session_is_callhome(const struct nc_session *session);
+
 /**@} Server Session */
 
 #ifdef __cplusplus