Need bigger log buffer to avoid message truncation

The help message of CRIU has grown in size and is truncated because the
size of the private buffer in log.c is too small.  This patch increases
the size of the buffer.

[ The "bad" message is the --help output one ]

Signed-off-by: Saied Kazemi <saied@google.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>