udhcpd: don't fail ARP check if returned MAC matches client's one

Also, do not unicast replies to yiaddr.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index 2dd3cd0..ab34b04 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -553,9 +553,10 @@
  * the client MUST send a DHCPDECLINE message to the server and restarts
  * the configuration process..." */
 						if (!arpping(packet.yiaddr,
-							    (uint32_t) 0,
-							    client_config.arp,
-							    client_config.interface)
+								NULL,
+								(uint32_t) 0,
+								client_config.arp,
+								client_config.interface)
 						) {
 							bb_info_msg("offered address is in use "
 								"(got ARP reply), declining");