ext/socket/ipsocket.c: Use SO_REUSEADDR for local_host/port

Sometimes ruby/spec fails when trying to specify local_host and
local_port for TCPSocket.open.

https://rubyci.org/logs/rubyci.s3.amazonaws.com/solaris11s-sunc/ruby-master/log/20190610T192504Z.fail.html.gz

ext/socket/ipsocket.c

@@ -99,6 +99,11 @@ init_inetsock_internal(struct inetsock_arg *arg)
 	}
 	else {
 	    if (lres) {
+#if !defined(_WIN32) && !defined(__CYGWIN__)
+		status = 1;
+		setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
+			   (char*)&status, (socklen_t)sizeof(status));
+#endif
 		status = bind(fd, lres->ai_addr, lres->ai_addrlen);
 		local = status;
 		syscall = "bind(2)";