MINOR: mux: add a "max_streams" method.

Add a new method to muxes, "max_streams", that returns the max number of
streams the mux can handle. This will be used to know if a mux is in use
or not.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index ae872f1..8d0851c 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -347,9 +347,16 @@
 {
 	struct h2c *h2c = conn->mux_ctx;
 
+	/* XXX Should use the negociated max concurrent stream nb instead of the conf value */
 	return (h2_settings_max_concurrent_streams - h2c->nb_streams);
 }
 
+static int h2_max_streams(struct connection *conn)
+{
+	/* XXX Should use the negociated max concurrent stream nb instead of the conf value */
+	return h2_settings_max_concurrent_streams;
+}
+
 
 /*****************************************************************/
 /* functions below are dedicated to the mux setup and management */
@@ -4825,6 +4832,7 @@
 	.detach = h2_detach,
 	.destroy = h2_destroy,
 	.avail_streams = h2_avail_streams,
+	.max_streams = h2_max_streams,
 	.shutr = h2_shutr,
 	.shutw = h2_shutw,
 	.show_fd = h2_show_fd,