Replace index_in_[sub]str_array with index_in_[sub]strings,

which scans thru "abc\0def\0123\0\0" type strings. Saves 250 bytes.

   text    data     bss     dec     hex filename
 781266    1328   11844  794438   c1f46 busybox_old
 781010    1328   11844  794182   c1e46 busybox_unstripped

networking/udhcp/dhcpc.c

@@ -200,7 +200,7 @@ int udhcpc_main(int argc, char **argv)
 		"timeout\0"       Required_argument "T"
 		"version\0"       No_argument       "v"
 		"retries\0"       Required_argument "t"
-		"\0";
+		;
 #endif
 	/* Default options. */
 	client_config.interface = "eth0";