udhcp[cd]: fix binding to network aliases. Closes 5432, 5438

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/networking/udhcp/socket.c b/networking/udhcp/socket.c
index a5220ba..a421069 100644
--- a/networking/udhcp/socket.c
+++ b/networking/udhcp/socket.c
@@ -80,6 +80,7 @@
 {
 	int fd;
 	struct sockaddr_in addr;
+	char *colon;
 
 	log1("Opening listen socket on *:%d %s", port, inf);
 	fd = xsocket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
@@ -88,10 +89,17 @@
 	if (setsockopt_broadcast(fd) == -1)
 		bb_perror_msg_and_die("SO_BROADCAST");
 
-	/* NB: bug 1032 says this doesn't work on ethernet aliases (ethN:M) */
+	/* SO_BINDTODEVICE doesn't work on ethernet aliases (ethN:M) */
+	colon = strrchr(inf, ':');
+	if (colon)
+		*colon = '\0';
+
 	if (setsockopt_bindtodevice(fd, inf))
 		xfunc_die(); /* warning is already printed */
 
+	if (colon)
+		*colon = ':';
+
 	memset(&addr, 0, sizeof(addr));
 	addr.sin_family = AF_INET;
 	addr.sin_port = htons(port);