pipe: increase the buffer size for pipe identifier

(00.312396)      4: Error (pipes.c:301): Not enough room for pipe 562178190 identifier string

Reported-by: Mr Jenkinks
Cc: Saied Kazemi <saied@google.com>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>