Update server.c

Fix multi addr bind: 
example ./ss-server -s 0 -s :: 
 2015-01-21 07:28:09 ERROR: bind: Address already in use
 2015-01-21 07:28:09 ERROR: Could not bind
 2015-01-21 07:28:09 ERROR: bind() error

src/server.c

@@ -167,6 +167,9 @@ int create_and_bind(const char *host, const char *port)
         }
 
         int opt = 1;
+
+        setsockopt(listen_sock, IPPROTO_IPV6, IPV6_V6ONLY, &opt, sizeof(opt));
+        
         setsockopt(listen_sock, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
 #ifdef SO_NOSIGPIPE
         setsockopt(listen_sock, SOL_SOCKET, SO_NOSIGPIPE, &opt, sizeof(opt));