busybox: Enable thread display

Our NETCONF stack is multithreaded and I'm tired of parsing procfs
manually.

Change-Id: I1f8d34030c88baf4e10aae61b7879cd017030417
diff --git a/board/czechlight/common/busybox-config b/board/czechlight/common/busybox-config
index dc6a9c5..db05ae0 100644
--- a/board/czechlight/common/busybox-config
+++ b/board/czechlight/common/busybox-config
@@ -1,2 +1,3 @@
 CONFIG_PING6=y
 CONFIG_TRACEROUTE6=y
+CONFIG_FEATURE_SHOW_THREADS=y