Upgrade libevent to release-2.1.10-stable

Test: None
Change-Id: I24e4275a07a6dcdd932056c7893a6aabdd786b8a
diff --git a/test/bench_http.c b/test/bench_http.c
index d20d3bc..80377ee 100644
--- a/test/bench_http.c
+++ b/test/bench_http.c
@@ -101,6 +101,9 @@
 		return (1);
 #endif
 
+	setbuf(stdout, NULL);
+	setbuf(stderr, NULL);
+
 	for (i = 1; i < argc; ++i) {
 		if (*argv[i] != '-')
 			continue;