Revert exi_zone to exi_zoneid, and install exi_ne backpointer

@@ -876,11 +876,11 @@
 
         avl_index_t             where;  /* used for avl_find()/avl_insert() */
 
         ASSERT(cr != NULL);
 
-        ASSERT3P(curzone, ==, exi->exi_zone);
+        ASSERT3P(curzone->zone_id, ==, exi->exi_zoneid);
         nag = nfsauth_get_zg();
 
         /*
          * Now check whether this client already
          * has an entry for this flavor in the cache