net: validate HWTSTAMP ioctl parameters

This patch adds a sanity check on the values provided by user space for
the hardware time stamping configuration. If the values lie outside of
the absolute limits, then the ioctl request will be denied.

Signed-off-by: Richard Cochran <richard.cochran@omicron.at>
Signed-off-by: David S. Miller <davem@davemloft.net>