udhcpc: do not use -t NUM for counting "select" packets, use 3

Otherwise, "-t 0" usage may end up sending them forever
if server does not respond.

function                                             old     new   delta
udhcpc_main                                         2846    2836     -10

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

networking/udhcp/dhcpc.c

@@ -1501,7 +1501,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
 				packet_num = 0;
 				continue;
 			case REQUESTING:
-				if (!discover_retries || packet_num < discover_retries) {
+				if (packet_num < 3) {
 					/* send broadcast select packet */
 					send_select(xid, server_addr, requested_ip);
 					timeout = discover_timeout;