Fix one wifi and ethernet concurrency bug

enable wifi and connect to a AP while ethernet cable plugged in.
wifi will be teared down.But driver is not stopped.After unplug
ethernet cable.It will failed to auto reconnect wifi.fix it here.

Change-Id: I1b0156cf89f26747ce67ebad2b4138e8d61f30df
Signed-off-by: Jianzheng Zhou <jianzheng.zhou@freescale.com>