MINOR: channel/htx: Add functions to forward a part or all HTX payload

The functions channel_htx_fwd_payload() and channel_htx_fwd_all() should now be
used to forward, respectively, a part of the HTX payload or all of it. These
functions forward data and update the first block position.
diff --git a/include/proto/channel.h b/include/proto/channel.h
index 3ebaf7f..d192c9b 100644
--- a/include/proto/channel.h
+++ b/include/proto/channel.h
@@ -912,7 +912,7 @@
 
 
 /* Forward all headers of an HTX message, starting from the SL to the EOH. This
- * function also updates the start-line position.
+ * function also updates the first block position.
  */
 static inline void channel_htx_fwd_headers(struct channel *chn, struct htx *htx)
 {
@@ -930,6 +930,33 @@
 	c_adv(chn, data);
 }
 
+/* Forward <data> bytes of payload of an HTX message. This function also updates
+ * the first block position.
+ */
+static inline void channel_htx_fwd_payload(struct channel *chn, struct htx *htx, size_t data)
+{
+	int32_t pos;
+
+	c_adv(chn, data);
+	for (pos = htx_get_first(htx); pos != -1; pos = htx_get_next(htx, pos)) {
+		uint32_t sz = htx_get_blksz(htx_get_blk(htx, pos));
+
+		if (data < sz)
+			break;
+		data -= sz;
+	}
+	htx->first = pos;
+}
+
+/* Forward all data of an HTX message. This function also updates the first
+ * block position.
+ */
+static inline void channel_htx_fwd_all(struct channel *chn, struct htx *htx)
+{
+	htx->first = -1;
+	c_adv(chn, htx->data - co_data(chn));
+}
+
 /*
  * Advance the channel buffer's read pointer by <len> bytes. This is useful
  * when data have been read directly from the buffer. It is illegal to call