BUG/MINOR: h2: properly report a stream error on RST_STREAM

We want to report such an error since H2 allows to differenciate
between an end of stream and an abort.

To be backported to 1.8.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index 7f58064..838ce95 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -1535,7 +1535,7 @@
 	h2c_stream_close(h2c, h2s);
 
 	if (h2s->cs) {
-		h2s->cs->flags |= CS_FL_EOS;
+		h2s->cs->flags |= CS_FL_EOS | CS_FL_ERROR;
 		/* recv is used to force to detect CS_FL_EOS that wake()
 		 * doesn't handle in the stream-int code.
 		 */