MINOR: proto-htx: Use channel_htx_fwd_headers() to forward 1xx responses

Instead of doing it by hand, we now call the dedicated function to do so.
diff --git a/src/proto_htx.c b/src/proto_htx.c
index 953b49f..dc0762d 100644
--- a/src/proto_htx.c
+++ b/src/proto_htx.c
@@ -1695,19 +1695,8 @@
 	 */
 	if (txn->status < 200 &&
 	    (txn->status == 100 || txn->status >= 102)) {
-		int32_t pos;
-
 		FLT_STRM_CB(s, flt_http_reset(s, msg));
-		for (pos = htx_get_first(htx); pos != -1; pos = htx_get_next(htx, pos)) {
-			struct htx_blk *blk = htx_get_blk(htx, pos);
-			enum htx_blk_type type = htx_get_blk_type(blk);
-
-			c_adv(rep, htx_get_blksz(blk));
-			if (type == HTX_BLK_EOH) {
-				htx->sl_pos = htx_get_next(htx, pos);
-				break;
-			}
-		}
+		channel_htx_fwd_headers(rep, htx);
 		msg->msg_state = HTTP_MSG_RPBEFORE;
 		txn->status = 0;
 		s->logs.t_data = -1; /* was not a response yet */