kerndat: initialize zero_page_pfn to -1
kerndat: initialize zero_page_pfn to -1

zero_page_pfn should be invalid if it isn't set to a real value.

zero is bad, because pagemap returns zero pfn-s for non-root users.

$ python test/zdtm.py run -t zdtm/static/env00 -k always -f h --user --norst
========================== Run zdtm/static/env00 in h ==========================
Start test
./env00 --pidfile=env00.pid --outfile=env00.out --envname=ENV_00_TEST
Run criu dump
Wait for zdtm/static/env00 to die for 0.100000
========================= Test zdtm/static/env00 PASS ==========================

$ ./crit/crit show test/dump/zdtm/static/env00/24/1/pagemap-24.img
{
    "magic": "PAGEMAP",
    "entries": [
        {
            "pages_id": 1
        },
        {
            "vaddr": "0x7ffcfd5ed000",
            "nr_pages": 2
        }
    ]
}

Signed-off-by: Andrew Vagin <74c05afa918858348d6db8037d82fa8124870113@virtuozzo.com>
Acked-by: Cyrill Gorcunov <7a1ea01eee6961eb1e372e3508c2670446d086f4@openvz.org>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@virtuozzo.com>

KKoukiou/criu-remote,KKoukiou/criu-remote,efiop/criu,efiop/criu,efiop/criu,KKoukiou/criu-remote,efiop/criu,eabatalov/criu,KKoukiou/criu-remote,eabatalov/criu,KKoukiou/criu-remote,eabatalov/criu,efiop/criu,KKoukiou/criu-remote,efiop/criu,eabatalov/criu,eabatalov/criu,eabatalov/criu