libxl: Set current memory value after successful balloon

The libxl driver does not set the new memory value in the active domain def
after a successful balloon. This results in the old memory value in
<currentMemory>. E.g.

virsh dumpxml test | grep currentMemory
  <currentMemory unit='KiB'>20971520</currentMemory>
virsh setmem test 16777216 --live
virsh dumpxml test | grep currentMemory
  <currentMemory unit='KiB'>20971520</currentMemory>

Set the new memory value in active domain def after a successful call to
libxl_set_memory_target().
Signed-off-by: NJim Fehlig <jfehlig@suse.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/libxl/libxl_driver.c

@@ -1676,6 +1676,7 @@ libxlDomainSetMemoryFlags(virDomainPtr dom, unsigned long newmem,
                                  " with libxenlight"), vm->def->id);
                 goto endjob;
             }
+            vm->def->mem.cur_balloon = newmem;
         }
 
         if (flags & VIR_DOMAIN_MEM_CONFIG) {