When setting the system time in VM, a RTC_CHANGE event will be reported.
However, if libvirt is restarted while the event is be reporting, the
event will be lost and we will get the old time (not the time we set in
VM) after rebooting the VM.
We save the delta time in QEMU and add a rtc-date-diff qmp to get the
delta time so that libvirt can get the latest time in VM according to
the qmp after libvirt is restarted.
Signed-off-by: Peng Liang <liangpeng10@huawei.com>
Signed-off-by: zhangxinhao <zhangxinhao1@huawei.com>
