5045 use atomic_{inc,dec}_* instead of atomic_add_*

*** 365,381 ****
   */
  
  static void
  fem_addref(struct fem_list *sp)
  {
!         atomic_add_32(&sp->feml_refc, 1);
  }
  
  static uint32_t
  fem_delref(struct fem_list *sp)
  {
!         return (atomic_add_32_nv(&sp->feml_refc, -1));
  }
  
  static struct fem_list *
  fem_get(struct fem_head *fp)
  {
--- 365,381 ----
   */
  
  static void
  fem_addref(struct fem_list *sp)
  {
!         atomic_inc_32(&sp->feml_refc);
  }
  
  static uint32_t
  fem_delref(struct fem_list *sp)
  {
!         return (atomic_dec_32_nv(&sp->feml_refc));
  }
  
  static struct fem_list *
  fem_get(struct fem_head *fp)
  {