MFC r244183 by glebius:

  Fix problem in r238990 (MFC'd in r240313).  The LLE_LINKED flag should be
  tested prior to entering llentry_free(), and in case if we lose the race,
  we should simply perform LLE_FREE_LOCKED().  Otherwise, if the race is
  lost by the thread performing arptimer(), it will remove two references
  from the lle instead of one.

  Reported by:	Ian FREISLICH <ianf clue.co.za>