iwlwifi: trace debug messages

Make iwlwifi record all debug messages into
tracing, even if debug_level is not enabled.
Due to the lack of APIs, the debug messages
are now recorded up to a max length of 100,
the only one above that is the RXON which is
not needed if you trace the commands as well
as it only dumps the command contents.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi W Guy <wey-yi.w.guy@intel.com>