message: added is_method_error method

Change-Id: I099744bed79e75da77e72167594c6ca14ef32209
Signed-off-by: Christian Andersen <c.andersen@kostal.com>
diff --git a/sdbusplus/message.hpp b/sdbusplus/message.hpp
index 053cd61..2d23ff3 100644
--- a/sdbusplus/message.hpp
+++ b/sdbusplus/message.hpp
@@ -96,6 +96,15 @@
         return sd_bus_message_get_signature(_msg.get(), true);
     }
 
+    /** @brief Check if message is a method error.
+     *
+     *  @return True - if message is a method error.
+     */
+    bool is_method_error()
+    {
+        return sd_bus_message_is_method_error(_msg.get(), nullptr);
+    }
+
     /** @brief Check if message is a method call for an interface/method.
      *
      *  @param[in] interface - The interface to match.