MINOR: proto_htx: Add some functions to handle HTX messages

More functions will come, but it is the minimum to switch HTX analyzers on the
HTX internal representation.
diff --git a/src/proto_http.c b/src/proto_http.c
index bd4221a..3481160 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -791,7 +791,7 @@
 	int tmp = TX_CON_WANT_KAL;
 
 	if (IS_HTX_STRM(s))
-		return htx_adjust_conn_mode(s, txn, msg);
+		return htx_adjust_conn_mode(s, txn);
 
 	if ((fe->options & PR_O_HTTP_MODE) == PR_O_HTTP_TUN ||
 	    (s->be->options & PR_O_HTTP_MODE) == PR_O_HTTP_TUN)