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

@@ -234,11 +234,11 @@
         tmp->nse_port = port;
         tmp->nse_nsh_lock = &ilbs->ilbs_nat_src[idx].nsh_lock;
         tmp->nse_refcnt = 1;
 
         (void) snprintf(arena_name, ARENA_NAMESZ, "ilb_ns_%u",
-            atomic_add_32_nv(&ilb_nat_src_instance, 1));
+            atomic_inc_32_nv(&ilb_nat_src_instance));
         if ((tmp->nse_port_arena = vmem_create(arena_name,
             (void *)NAT_PORT_START, NAT_PORT_SIZE, 1, NULL, NULL, NULL, 1,
             VM_SLEEP | VMC_IDENTIFIER)) == NULL) {
                 kmem_free(tmp, sizeof (*tmp));
                 return (NULL);