idpf: protect shutdown from reset

Before the referenced commit, the shutdown just called idpf_remove(),
this way IDPF_REMOVE_IN_PROG was protecting us from the serv_task
rescheduling reset. Without this flag set the shutdown process is
vulnerable to HW reset or any other triggering conditions (such as
default mailbox being destroyed).

When one of conditions checked in idpf_service_task becomes true,
vc_event_task can be rescheduled during shutdown, this leads to accessing
freed memory e.g. idpf_req_rel_vector_indexes() trying to read
vport->q_vector_idxs. This in turn causes the system to become defunct
during e.g. systemctl kexec.

Considering using IDPF_REMOVE_IN_PROG would lead to more heavy shutdown
process, instead just cancel the serv_task before cancelling
adapter->serv_task before cancelling adapter->vc_event_task to ensure that
reset will not be scheduled while we are doing a shutdown.

Fixes: 4c9106f4 ("idpf: fix adapter NULL pointer dereference on reboot")
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Samuel Salin <Samuel.salin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>