kerndat: check the lock field in fdinfo (v2)

Starting with the 4.1 kernel, fdinfo contains information about file
locks.

v2: s/has_lock/has_fdinfo_lock/
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>