Don't try to do IPV6_V6ONLY on OpenBSD either.

setsockopt(3) returns an error if passing 0 to this option (which
we do if no address family is specified when we bind to the wildcard
address, say by invoking "iperf3 -s" with no other options).  This
is because OpenBSD explicitly does not support IPv4-mapped addresses,
so even though the IPV6_V6ONLY socket options exists, it only works
with a non-zero argument.

Fixes #196.

src/iperf_sctp.c

@@ -155,7 +155,7 @@ iperf_sctp_listen(struct iperf_test *test)
         return -1;
     }
 
-#ifdef IPV6_V6ONLY
+#if defined(IPV6_V6ONLY) && !defined(__OpenBSD__)
     if (test->settings->domain == AF_UNSPEC || test->settings->domain == AF_INET6) {
         if (test->settings->domain == AF_UNSPEC)
             opt = 0;

src/iperf_tcp.c

@@ -216,7 +216,7 @@ iperf_tcp_listen(struct iperf_test *test)
             i_errno = IEREUSEADDR;
             return -1;
         }
-#ifdef IPV6_V6ONLY
+#if defined(IPV6_V6ONLY) && !defined(__OpenBSD__)
 	if (test->settings->domain == AF_UNSPEC || test->settings->domain == AF_INET6) {
 	    if (test->settings->domain == AF_UNSPEC)
 		opt = 0;

src/net.c

@@ -146,9 +146,12 @@ netannounce(int domain, int proto, char *local, int port)
     /*
      * If we got an IPv6 socket, figure out if it should accept IPv4
      * connections as well.  We do that if and only if no address
-     * family was specified explicitly.
+     * family was specified explicitly.  Note that we can only
+     * do this if the IPV6_V6ONLY socket option is supported.  Also,
+     * OpenBSD explicitly omits support for IPv4-mapped addresses,
+     * even though it implements IPV6_V6ONLY.
      */
-#ifdef IPV6_V6ONLY
+#if defined(IPV6_V6ONLY) && !defined(__OpenBSD__)
     if (res->ai_family == AF_INET6 && (domain == AF_UNSPEC || domain == AF_INET6)) {
 	if (domain == AF_UNSPEC)
 	    opt = 0;