CLEANUP: mux-h2: fix end-of-stream flag name when processing headers

In h2c_decode_headers() we mistakenly check for H2_F_DATA_END_STREAM
while we should check for H2_F_HEADERS_END_STREAM. Both have the same
value (1) but better stick to the correct flag.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index 5803a84..e0859b9 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -3332,7 +3332,7 @@
 	}
 
 	/* OK now we have our header list in <list> */
-	msgf = (h2c->dff & H2_F_DATA_END_STREAM) ? 0 : H2_MSGF_BODY;
+	msgf = (h2c->dff & H2_F_HEADERS_END_STREAM) ? 0 : H2_MSGF_BODY;
 
 	if (htx) {
 		/* HTX mode */