ptp: tg3: convert to the 64 bit get/set time methods.

The device appears to use a 64 bit nanoseconds register, and so with
this patch the driver should be ready for the year 2038.

Compile tested only.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>