board/common: silence libyang warnings leaking to console

Fixes #1373

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Author: troglobit

board/common/rootfs/etc/finit.d/available/restconf.conf

@@ -1,3 +1,3 @@
-service name:rousette notify:none log:console <pid/confd> env:/etc/default/confd \
+service name:rousette notify:none log:null <pid/confd> env:/etc/default/confd \
 	[12345] rousette --syslog -t $CONFD_TIMEOUT \
 	-- RESTCONF server