MEDIUM: h1: let the caller pass the initial parser's state

This way the caller controls if it's the request or response which has
to be used, and it will allow to restart after an incomplete parsing.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index 4d9a7bc..d842cd8 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -3103,6 +3103,8 @@
 	 * block does not wrap and we can safely read it this way without
 	 * having to realign the buffer.
 	 */
+	h1m->state = H1_MSG_RPBEFORE;
+	h1m->next  = 0;
 	ret = h1_headers_to_hdr_list(b_peek(buf, ofs), b_peek(buf, ofs) + max,
 	                             list, sizeof(list)/sizeof(list[0]), h1m, NULL);
 	if (ret <= 0) {