iwlwifi: mvm: ROC - bug fixes around time events and locking

Don't add the time event to the list. We added it several
times the same time event, which leads to an infinite loop
when walking the list.

Since we (currently) don't support more than one ROC for STA
vif at a time, enforce this and don't add the time event
to any list.

We were also missing the locking of the mutex which led to
a lockdep splat - fix that.

Signed-off-by: Matti Gottlieb <matti.gottlieb@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>