DNS: Don't apply search domains to PTR lookups

This lessens the load on upstream DNS servers (and it was just nonsensical).

Signed-off-by: Tim Hockin <thockin@google.com>

libc/inet/resolv.c

@@ -1264,7 +1264,7 @@ int __dns_lookup(const char *name,
 	int variant = -1;  /* search domain to append, -1: none */
 	int local_ns_num = -1; /* Nth server to use */
 	int local_id = local_id; /* for compiler */
-	int sdomains;
+	int sdomains = 0;
 	bool ends_with_dot;
 	sockaddr46_t sa;
 
@@ -1302,7 +1302,9 @@ int __dns_lookup(const char *name,
 		 * or do other Really Bad Things. */
 		__UCLIBC_MUTEX_LOCK(__resolv_lock);
 		__open_nameservers();
-		sdomains = __searchdomains;
+		if (type != T_PTR) {
+			sdomains = __searchdomains;
+		}
 		lookup[name_len] = '\0';
 		if ((unsigned)variant < sdomains) {
 			/* lookup is name_len + 1 + MAXLEN_searchdomain + 1 long */