allow suppression of default client-id.  fixes bug 000037.  allows
busybox to match kernel and u-boot behavior with respect to client-id.
diff --git a/networking/udhcp/clientpacket.c b/networking/udhcp/clientpacket.c
index c5e1c21..2695b06 100644
--- a/networking/udhcp/clientpacket.c
+++ b/networking/udhcp/clientpacket.c
@@ -76,7 +76,8 @@
 
 	init_header(packet, type);
 	memcpy(packet->chaddr, client_config.arp, 6);
-	add_option_string(packet->options, client_config.clientid);
+	if (client_config.clientid)
+	    add_option_string(packet->options, client_config.clientid);
 	if (client_config.hostname) add_option_string(packet->options, client_config.hostname);
 	if (client_config.fqdn) add_option_string(packet->options, client_config.fqdn);
 	add_option_string(packet->options, (uint8_t *) &vendor_id);