iwm - Clear Time Event active state, when receiving End Notification.

• This hopefully avoids some firmware panics, I was occasionally seeing,

when iwm disconnects upon losing signal to an access point at some point.

• This is synchronizing the if_iwm_time_event.c file a bit more from the

corresponding Linux iwlwifi/mvm/time-event.c.

Taken-From: Linux iwlwifi

Submitted by: Augustin Cavalier <waddlesplash@gmail.com> (Haiku)
Obtained from: DragonFlyBSD (e8cb71584a6a72232c13151d60e57f7f229220eb)