Rename iperf binary to iperf3

Change-Id: I41e4d1e9e4356d0fd723f9aae382086f94d30fc9
diff --git a/BUILD.gn b/BUILD.gn
index 2c510b4..45e7976 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -32,7 +32,7 @@
   include_dirs = [ "src" ]
 }
 
-executable("iperf") {
+executable("iperf3") {
   sources = [
     "src/cjson.c",
     "src/iperf_api.c",