>From the commit 64e74fab ("parasite: handle errors while a transport
socket is being created"), we have futex in parasite init args to
synchronize parasite and criu during initialization.
And man futex(2): "On all platforms, futexes are four-byte integers that
must be aligned on a four-byte boundary."
This is checked by kernel in get_futex_key():
	if (unlikely((address % sizeof(u32)) != 0))
		return -EINVAL;

So, we need to align parasite arguments on four bytes, while mapping
of parasite blob on page-aligned address will guarantee that it'll
be aligned on four bytes in memory.

Fixes:
(00.013468) -----------------------
(00.013470) Putting tsock into pid 22043
(00.014024) Error (criu/parasite-syscall.c:541): futex() returned an unexpected error: -22
(00.014026) Error (criu/parasite-syscall.c:541): BUG at criu/parasite-syscall.c:541

Cc: Andrew Vagin <avagin@virtuozzo.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>