iwlwifi: mvm: dynamically update tsf_id

Currently, the MAC context tsf_id assignment and the master/slave
relations are determined only when a new vif is added, as part
of the MAC context resource allocation. However, at this stage, the
beacon interval is not known, and thus could not be taken into account
in the master-slave algorithm.

To fix this, recalculate the MAC context tsf_id assignment,
just before the MAC context is activated, i.e., just before
a station VMAC is configured to associated and before an AP
VMAC is started.

Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>