lxc: fix setmem effect on a running LXC machine

When user calls setmem on a running LXC machine, we do update its cgroup
entry, however we neither update domain's runtime XML nor
we update our internal structures and this patch fixes it.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1131919

src/lxc/lxc_driver.c

@@ -749,6 +749,10 @@ static int lxcDomainSetMemoryFlags(virDomainPtr dom, unsigned long newmem,
                                "%s", _("Failed to set memory for domain"));
                 goto cleanup;
             }
+
+            vm->def->mem.cur_balloon = newmem;
+            if (virDomainSaveStatus(driver->xmlopt, cfg->stateDir, vm) < 0)
+                goto cleanup;
         }
 
         if (flags & VIR_DOMAIN_AFFECT_CONFIG) {