Another iteration on issue #193, fixes -B with some TCP tests.

When we do TCP tests and specify the socket buffer size, MSS, or
TCP no delay option, the iperf3 server destroys the socket it was
using to listen for the control connection and opens up a new
listening socket for the test's data connections.  This is (I think)
to make sure that the data connections all have the correct TCP
parameters.

When we re-create the listening socket, we also need to go through
the binding logic again (with all of the address family selectiion,
etc. goop).  The bug fixes that were a part of issue #193 need to
be ported to this code as well.

This problem only affects TCP tests, because for other protocols,
the listening socket for data cannot be the same listening sock as
for the control connection.

While here, add some comments so anybody trying to understand this
code will have an easier time.

Based on patch by:	@i2aaron

src/iperf_tcp.c

@@ -125,13 +125,33 @@ iperf_tcp_listen(struct iperf_test *test)
 
     s = test->listener;
 
+    /*
+     * If certain parameters are specified (such as socket buffer
+     * size), then throw away the listening socket (the one for which
+     * we just accepted the control connection) and recreate it with
+     * those parameters.  That way, when new data connections are
+     * set, they'll have all the correct parameters in place.
+     *
+     * It's not clear whether this is a requirement or a convenience.
+     */
     if (test->no_delay || test->settings->mss || test->settings->socket_bufsize) {
         FD_CLR(s, &test->read_set);
         close(s);
 
         snprintf(portstr, 6, "%d", test->server_port);
         memset(&hints, 0, sizeof(hints));
-        hints.ai_family = (test->settings->domain == AF_UNSPEC ? AF_INET6 : test->settings->domain);
+
+	/*
+	 * If binding to the wildcard address with no explicit address
+	 * family specified, then force us to get an AF_INET6 socket.
+	 * More details in the comments in netanounce().
+	 */
+	if (test->settings->domain == AF_UNSPEC && !test->bind_address) {
+	    hints.ai_family = AF_INET6;
+	}
+	else {
+	    hints.ai_family = test->settings->domain;
+	}
         hints.ai_socktype = SOCK_STREAM;
         hints.ai_flags = AI_PASSIVE;
         if (getaddrinfo(test->bind_address, portstr, &hints, &res) != 0) {
@@ -216,11 +236,17 @@ iperf_tcp_listen(struct iperf_test *test)
             i_errno = IEREUSEADDR;
             return -1;
         }
+
+	/*
+	 * If we got an IPv6 socket, figure out if it shoudl accept IPv4
+	 * connections as well.  See documentation in netannounce() for
+	 * more details.
+	 */
 #if defined(IPV6_V6ONLY) && !defined(__OpenBSD__)
-	if (test->settings->domain == AF_UNSPEC || test->settings->domain == AF_INET6) {
+	if (res->ai_family == AF_INET6 && (test->settings->domain == AF_UNSPEC || test->settings->domain == AF_INET)) {
 	    if (test->settings->domain == AF_UNSPEC)
 		opt = 0;
-	    else if (test->settings->domain == AF_INET6)
+	    else 
 		opt = 1;
 	    if (setsockopt(s, IPPROTO_IPV6, IPV6_V6ONLY, 
 			   (char *) &opt, sizeof(opt)) < 0) {