wlan: Handle session leak during change interface

Currently in change interface, the status of the interface is not being
checked before initializing the mode. If the interface is down, one more
session will be created when interface up is triggered. In this case,
the session created during the change interface will not be deleted.

To handle this, check for interface up before initializing the mode
during change interface.

Change-Id: Ifbcbfa7249e3ecacc4259000aa7558eeecdfb5f3
CRs-Fixed: 2782058