MINOR: h2: make struct h2_ops static

There's no reason to export this descriptor, it used to be needed during
early H2 development and will complicate porting to HTX.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index 1971792..b1bf62b 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -3811,7 +3811,7 @@
 /***************************************/
 
 /* The mux operations */
-const struct mux_ops h2_ops = {
+static const struct mux_ops h2_ops = {
 	.init = h2_init,
 	.wake = h2_wake,
 	.snd_buf = h2_snd_buf,