tools/libxl: introduce libxl__domain_common_switch_qemu_logdirty()

tools/libxl: introduce libxl__domain_common_switch_qemu_logdirty()

Secondary vm is running in COLO mode, we need to send secondary
vm's dirty page information to primary host at checkpoint, so we
have to enable qemu logdirty on secondary.

libxl__domain_suspend_common_switch_qemu_logdirty() is to enable
qemu logdirty. But it uses libxl__domain_save_state, and calls
libxl__xc_domain_saverestore_async_callback_done() before exits.
This can not be used for secondary vm.

Update libxl__domain_suspend_common_switch_qemu_logdirty() to
introduce a new API libxl__domain_common_switch_qemu_logdirty().
This API only uses libxl__logdirty_switch, and calls
lds->callback before exits. This new API will be used by the patch:
  secondary vm suspend/resume/checkpoint codes

Signed-off-by: Yang Hongyang <hongyang.yang@easystack.cn>
Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Changlong Xie <xiecl.fnst@cn.fujitsu.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>