Moved check if packet already encoded to ike_sa, avoids message() hook invocation twice

src/libcharon/encoding/message.h

@@ -257,6 +257,13 @@ struct message_t {
 	 */
 	status_t (*generate) (message_t *this, aead_t *aead, packet_t **packet);
 
+	/**
+	 * Check if the message has already been encoded using generate().
+	 *
+	 * @return			TRUE if message has been encoded
+	 */
+	bool (*is_encoded)(message_t *this);
+
 	/**
 	 * Gets the source host informations.
 	 *