staging/lustre: use 64-bit timestamps for selftest

The wire protocol for the ping uses a 64-bit seconds/microseconds
pair, but this won't work when one side uses a 32-bit timeval
to look up the current time beyond 2038.

This changes the code to use ktime_get_real_ts64() to create
a timestamp that has the right format on all machines.

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>