When user try to use linux command brctl stp br-lan on/off
to set up the stp, it will cause linux go hung.

This is because when rstp is not enabled, the commands brctl stp
br-lan on will avoke rstp, the rstp will call this command again,
and in this command, it use a lock, it cause deadlock, make the
kernel hung.

in this fixes, the command won't run the rstp again, so it won't
go into deadlock.

Change-Id: I4b7322f976ec00c8c65219a2be43a7173858b917
Signed-off-by: Zhu Ken <guigenz@codeaurora.org>