parse: prefault config file with MAP_POPULATE
parse: prefault config file with MAP_POPULATE

When we call lxc_file_for_each_line_mmap() we will always parse the
whole config file. Prefault it in case it is really long to optimize
performance.

Signed-off-by: Christian Brauner <48455ab3070520a2d174545c7239d6d0fabd9a83@ubuntu.com>

ss1h2a3tw/lxc,hallyn/lxc,hallyn/lxc,caglar10ur/lxc,hallyn/lxc,ss1h2a3tw/lxc,caglar10ur/lxc,ss1h2a3tw/lxc,caglar10ur/lxc