ipc_ns: allocate enough memrory for the buffer

==22653== Syscall param read(buf) points to unaddressable byte(s)
==22653==    at 0x50480B0: __read_nocancel (in /usr/lib64/libpthread-2.17.so)
==22653==    by 0x40CF7C: parasite_dump_pages_seized (mem.c:244)
==22653==    by 0x41681D: cr_dump_tasks (cr-dump.c:1533)
==22653==    by 0x40448C: main (crtools.c:309)

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>