Added software timestamping ability. Tested with linuxptp and synchronized
clocks to an average of less than 200 microseconds on 10 megabit ethernet.

Tested on both Vortex and Boomerang models.
Signed-off-by: Matthew Whitehead <tedheadster@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>