net: ethernet: ti: netcp_ethss: use cpts to check if packet needs timestamping

There is cpts function to check if packet can be timstamped with cpts.
Seems that ptp_classify_raw cover all cases listed with "case".

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>