staging/lustre: use 64-bit time LNetCtl()

This ioctl function passes a 64-bit time argument but then performs
a computation with a 32-bit get_seconds() value.

In order to avoid overflow here, this changes the code to use
64-bit math and ktime_get_real_seconds().

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>