daemon: unbreak NO_IPV6 build regression

When 01cec54e (daemon: deglobalize hostname information, 2015-03-07)
wrapped the global variables such as hostname inside a struct, it
forgot to convert one location that spelled "hostname" that needs to
be updated to "hi->hostname".

This was inside NO_IPV6 block, and was not caught by anybody.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

daemon.c

@@ -633,7 +633,7 @@ static void lookup_hostname(struct hostinfo *hi)
 		char **ap;
 		static char addrbuf[HOST_NAME_MAX + 1];
 
-		hent = gethostbyname(hostname.buf);
+		hent = gethostbyname(hi->hostname.buf);
 		if (hent) {
 			ap = hent->h_addr_list;
 			memset(&sa, 0, sizeof sa);