udhcpc: add -o "do not request options by default" switch
(by L. Gabriel Somlo <somlo AT cmu.edu>)

function                                             old     new   delta
udhcpc_main                                         2513    2554     +41
static.udhcpc_longopts                               226     247     +21
add_param_req_option                                 119     132     +13
packed_usage                                       23952   23964     +12
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/0 up/down: 87/0)               Total: 87 bytes

diff --git a/networking/udhcp/clientpacket.c b/networking/udhcp/clientpacket.c
index 29d0d9a..f826c1b 100644
--- a/networking/udhcp/clientpacket.c
+++ b/networking/udhcp/clientpacket.c
@@ -62,17 +62,20 @@
 	int end = end_option(packet->options);
 	int i, len = 0;
 
-	packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
 	for (i = 0; (c = dhcp_options[i].code) != 0; i++) {
-		if ((dhcp_options[i].flags & OPTION_REQ)
+		if (((dhcp_options[i].flags & OPTION_REQ)
+                     && !client_config.no_default_options)
 		 || (client_config.opt_mask[c >> 3] & (1 << (c & 7)))
 		) {
 			packet->options[end + OPT_DATA + len] = c;
 			len++;
 		}
 	}
-	packet->options[end + OPT_LEN] = len;
-	packet->options[end + OPT_DATA + len] = DHCP_END;
+	if (len) {
+		packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
+		packet->options[end + OPT_LEN] = len;
+		packet->options[end + OPT_DATA + len] = DHCP_END;
+	}
 }
 
 
@@ -107,7 +110,9 @@
 	/* Explicitly saying that we want RFC-compliant packets helps
 	 * some buggy DHCP servers to NOT send bigger packets */
 	add_simple_option(packet.options, DHCP_MAX_SIZE, htons(576));
+
 	add_param_req_option(&packet);
+
 	bb_info_msg("Sending discover...");
 	return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 			SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
@@ -125,8 +130,8 @@
 
 	add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 	add_simple_option(packet.options, DHCP_SERVER_ID, server);
-
 	add_param_req_option(&packet);
+
 	addr.s_addr = requested;
 	bb_info_msg("Sending select for %s...", inet_ntoa(addr));
 	return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,