udhcpc: Add support to change default interface name

Signed-off-by: Andre Kalb <Andre.Kalb@sma.de>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index 98720b4..922c71e 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -1196,7 +1196,7 @@
 //usage:       "	[-i IFACE]"IF_FEATURE_UDHCP_PORT(" [-P PORT]")" [-s PROG] [-p PIDFILE]\n"
 //usage:       "	[-oC] [-r IP] [-V VENDOR] [-F NAME] [-x OPT:VAL]... [-O OPT]..."
 //usage:#define udhcpc_full_usage "\n"
-//usage:     "\n	-i IFACE	Interface to use (default eth0)"
+//usage:     "\n	-i IFACE	Interface to use (default "CONFIG_UDHCPC_DEFAULT_INTERFACE")"
 //usage:	IF_FEATURE_UDHCP_PORT(
 //usage:     "\n	-P PORT		Use PORT (default 68)"
 //usage:	)
@@ -1265,7 +1265,7 @@
 	/* Default options */
 	IF_FEATURE_UDHCP_PORT(SERVER_PORT = 67;)
 	IF_FEATURE_UDHCP_PORT(CLIENT_PORT = 68;)
-	client_data.interface = "eth0";
+	client_data.interface = CONFIG_UDHCPC_DEFAULT_INTERFACE;
 	client_data.script = CONFIG_UDHCPC_DEFAULT_SCRIPT;
 	client_data.sockfd = -1;
 	str_V = "udhcp "BB_VER;