libxc/save: refactor of send_domain_memory_live()

libxc/save: refactor of send_domain_memory_live()

Split the send_domain_memory_live() into three helper function:
  - send_memory_live()  do the actually live send
  - suspend_and_send_dirty() suspend the guest and send dirty pages
  - send_memory_verify()
The motivation of this is that when we send checkpointed stream, we
will skip the actually live part.

Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>