[iwm] Ignore IWM_DEBUG_LOG_MSG notifications.
- Firmware versions 21 and 22 generate some IWM_DEBUG_LOG_MSG notifications, which seem to be harmless. Avoid spamming the system log with "frame ... UNHANDLED (this should not happen)" messages.
Obtained from: dragonflybsd.git dda889ac57d8e5b46bb1b1ecf53c17a18481c7c8