usbip: use monotonic timestamps

This gets rid of the deprecated do_gettimeofday() function in usbip.
The comment above vgadget_get_frame() mentions that it suffers
from issues with the time jumps due to suspend and settimeofday,
so I'm changing it to use ktime_get_ts64() to use monotonic times
that don't have this problem.

I couldn't tell whether we should use CLOCK_MONOTONIC or
CLOCK_MONOTONIC_RAW here, the difference being the exact rate
when correcting for NTP. I picked monotonic time since it doesn't
change the speed to the existing code and should be better
synchronized with other machines we talk to.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>