Add support to create IKE fragments

All fragments currently use the same fragment ID (1) as that's what
other implementations are doing.

src/libcharon/encoding/payloads/fragment_payload.c

@@ -206,3 +206,20 @@ fragment_payload_t *fragment_payload_create()
 	this->payload_length = get_header_length(this);
 	return &this->public;
 }
+
+/*
+ * Described in header
+ */
+fragment_payload_t *fragment_payload_create_from_data(u_int8_t num, bool last,
+													  chunk_t data)
+{
+	private_fragment_payload_t *this;
+
+	this = (private_fragment_payload_t*)fragment_payload_create();
+	this->fragment_id = 1;
+	this->fragment_number = num;
+	this->flags |= (last ? LAST_FRAGMENT : 0);
+	this->data = chunk_clone(data);
+	this->payload_length = get_header_length(this) + data.len;
+	return &this->public;
+}

src/libcharon/encoding/payloads/fragment_payload.h

@@ -78,4 +78,17 @@ struct fragment_payload_t {
  */
 fragment_payload_t *fragment_payload_create();
 
+/**
+ * Creates a fragment payload from the given data.  All fragments currently
+ * have the same fragment ID (1), which seems what other implementations are
+ * doing.
+ *
+ * @param num		fragment number (first one should be 1)
+ * @param last		TRUE to indicate that this is the last fragment
+ * @param data		fragment data (gets cloned)
+ * @return			fragment_payload_t object
+ */
+fragment_payload_t *fragment_payload_create_from_data(u_int8_t num, bool last,
+													  chunk_t data);
+
 #endif /** FRAGMENT_PAYLOAD_H_ @}*/