iwlwifi: trans: support a callback for ASYNC commands

iwlwifi: trans: support a callback for ASYNC commands

This allows the op_mode to request from the transport to
call a callback when an ASYNC commands is completed by
the firmware. The same callback will be called for all the
commands. Pass the command whose response triggers the
callback as a parameter to the callback itself.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>