compel/infect: fix out-of-bounds parasite memcpy()

We need to copy only parasite, do copy page-aligned size,
which will copy part of CRIU binary, that follows parasite
blob. That will cross red-zones and fire asan error.

travis-ci: success for series starting with [1/6] compel/infect: fix out-of-bounds parasite memcpy()
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>