* Add in a comment about ar5416InitUserSettings() potentially

* Add in a comment about ar5416InitUserSettings() potentially
  modifying AR_DIAG_SW.

  There's a hardware workaround which sets disabling some errors
  early at startup and clears said bits before the PCU begins
  receiving - it does this to avoid RX descriptor status errors.

  It's possible these bits aren't being completely properly twiddled
  in all instances; but in particular if the diag_reg HAL variable
  is set it won't be setting these bits correctly. I'll review this
  at some point.

 * Disable multicast search on mac address and key id - the driver
   doesn't use it at the moment and thus adhoc may be broken for
   merlin and later.

* Change this to be for Merlin 1.0 (which from what I understand
  wasn't ever publicly released) to be more correct.