e100: enable transmit time stamping.

This patch enables software (and phy device) transmit time stamping.
Tested on an old PIII laptop with built in NIC.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>