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

@@ -1275,11 +1275,11 @@
                 ASSERT(kmem_lp_arena != NULL);
                 ASSERT(asize >= size);
 
                 if (lpthrt != 0) {
                         /* try to update the throttle value */
-                        lpthrt = atomic_add_long_nv(lpthrtp, 1);
+                        lpthrt = atomic_inc_ulong_nv(lpthrtp);
                         if (lpthrt >= segkmem_lpthrottle_max) {
                                 lpthrt = atomic_cas_ulong(lpthrtp, lpthrt,
                                     segkmem_lpthrottle_max / 4);
                         }