Currently api hdd_wmm_free_context free the hdd_wmm context and
this api is getting invoked from several places without disabling
the inactivity timer.
Since the timer is not disabled, when hdd_wmm_inactivity_timer_cb
is invoked it tries to access the hdd_wmm context which is already
freed and the memory is reallocated to someone else resulting to
undefined behaviour.
To address this issue, disable hdd_wmm_inactivity timer before
calling hdd_wmm_free_context function and add a check for
hdd_wmm context in hdd_wmm_inactivity_timer_cb, if hdd_wmm context
is NULL don't proceed further and return.
Change-Id: Ib085c70b3e5a57b5cd494bc2cd21edd0580c16c4
CRs-Fixed: 2233987
80b01b55e4