libxc/save: reuse send_dirty_pages() in send_all_pages()

libxc/save: reuse send_dirty_pages() in send_all_pages()

introduce bitmap_set() to set the entire bitmap.
in send_all_pages(), set the entire bitmap and call send_dirty_pages().

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>