Implement decryptPayload and invoke it when unflattening the packet

Change-Id: I52b283c9390e43c89b84d0617cebaf4938dad881
Signed-off-by: Tom Joseph <tomjoseph@in.ibm.com>
diff --git a/message_parsers.hpp b/message_parsers.hpp
index 9403687..774b985 100644
--- a/message_parsers.hpp
+++ b/message_parsers.hpp
@@ -195,6 +195,19 @@
                       const Message& message,
                       size_t payloadLen);
 
+/*
+ * @brief Decrypt the encrypted payload in the incoming IPMI packet
+ *
+ * @param[in] packet - Incoming IPMI packet
+ * @param[in] message - IPMI Message populated from the incoming packet
+ * @param[in] payloadLen - Length of encrypted IPMI payload
+ *
+ * @return on successful completion, return the plain text payload
+ */
+std::vector<uint8_t> decryptPayload(const std::vector<uint8_t>& packet,
+                                    const Message& message,
+                                    size_t payloadLen);
+
 } // namespace internal
 
 } // namespace ipmi20parser