Only do the IPV6_V6ONLY setsockopt(3) stuff if that option is available.

Should fix #177, in which compilation failed on older Solaris systems
that didn't have it.  This is a different approach than a patch
suggested in that issue.

Weakly regression-tested on other platforms (test this by specifying
-6, -4, or neither to the server when binding to the wildcard address,
and seeing if a client can connect with various of -6, -4, or neither).

src/iperf_sctp.c

@@ -155,6 +155,7 @@ iperf_sctp_listen(struct iperf_test *test)
         return -1;
     }
 
+#ifdef IPV6_V6ONLY
     if (test->settings->domain == AF_UNSPEC || test->settings->domain == AF_INET6) {
         if (test->settings->domain == AF_UNSPEC)
             opt = 0;
@@ -168,6 +169,7 @@ iperf_sctp_listen(struct iperf_test *test)
 	    return -1;
 	}
     }
+#endif /* IPV6_V6ONLY */
 
     opt = 1;
     if (setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) < 0) {

src/iperf_tcp.c

@@ -216,6 +216,7 @@ iperf_tcp_listen(struct iperf_test *test)
             i_errno = IEREUSEADDR;
             return -1;
         }
+#ifdef IPV6_V6ONLY
 	if (test->settings->domain == AF_UNSPEC || test->settings->domain == AF_INET6) {
 	    if (test->settings->domain == AF_UNSPEC)
 		opt = 0;
@@ -231,6 +232,7 @@ iperf_tcp_listen(struct iperf_test *test)
 		return -1;
 	    }
 	}
+#endif /* IPV6_V6ONLY */
 
         if (bind(s, (struct sockaddr *) res->ai_addr, res->ai_addrlen) < 0) {
 	    saved_errno = errno;

src/net.c

@@ -143,12 +143,12 @@ netannounce(int domain, int proto, char *local, int port)
 	freeaddrinfo(res);
 	return -1;
     }
-
     /*
      * 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.
      */
+#ifdef IPV6_V6ONLY
     if (res->ai_family == AF_INET6 && (domain == AF_UNSPEC || domain == AF_INET6)) {
 	if (domain == AF_UNSPEC)
 	    opt = 0;
@@ -161,6 +161,7 @@ netannounce(int domain, int proto, char *local, int port)
 	    return -1;
 	}
     }
+#endif /* IPV6_V6ONLY */
 
     if (bind(s, (struct sockaddr *) res->ai_addr, res->ai_addrlen) < 0) {
         close(s);