Keep xsave sizes in image to be sure that on restore the application
won't override memory out of xsave frame size if been calling xsave
instruction directly.

Here are some details: while been testing vz7 containers migration
we've noticed that sometime applications do crash after restore,
what is worse such execution abort may happen not immediately
after the restore but after passing some time. After spending
a lot of time we discovered that it is due to the fact that
the migration is directed from an old cpu to a modern one
which has extensions such as mpx. In result libc has cached
small xsave size and then after restore any direct call to
xsave instruction overwrite memory which is allocated with
size less than needed.

Thus we save xsave frame size in image and require it to
match to prevent such situation.
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Reviewed-by: Dmitry Safonov <0x7f454c46@gmaill.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>