Idle TCP connection hangs/DoSes the server

https://github.com/esnet/iperf/issues/788

diff -Nur iperf-3.10.old/src/iperf_server_api.c iperf-3.10/src/iperf_server_api.c

--- iperf-3.10.old/src/iperf_server_api.c	2021-05-27 02:13:00.000000000 +0400

+++ iperf-3.10/src/iperf_server_api.c	2021-10-31 15:15:36.761797841 +0400

@@ -130,6 +130,12 @@

             return -1;

         }

+	struct timeval timeout;

+	timeout.tv_sec = 5;

+	timeout.tv_usec = 0;

+	setsockopt (s, SOL_SOCKET, SO_RCVTIMEO, (const char *)&timeout, sizeof(timeout));

+	setsockopt (s, SOL_SOCKET, SO_SNDTIMEO, (const char *)&timeout, sizeof(timeout));

+

         if (Nread(test->ctrl_sck, test->cookie, COOKIE_SIZE, Ptcp) < 0) {

             i_errno = IERECVCOOKIE;

             return -1;