dump: save all vdso pages (v2)
dump: save all vdso pages (v2)

If a vdso page was not accessed before dump, it's not present
and now it doesn't save in a dump image.
The vdso area is restored as VMA_ANON, it isn't an actual vdso more,
so when a not-present vdso page is accessed, a zero page would be mapped.

For this reason we should save all vdso pages in a image.

v2: make code more clear

Signed-off-by: Andrey Vagin <74c05afa918858348d6db8037d82fa8124870113@openvz.org>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

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