sfc: support separate PTP and general timestamping
Support MC_CMD_PTP_OUT_GET_TIMESTAMP_CORRECTIONS_V2. Extract general
timestamp corrections in addition to PTP corrections. Apply receive
timestamp corrections for general datapath receive timestamping, and
correspondingly for transmit.
Signed-off-by: Laurence Evans <levans@solarflare.com> Signed-off-by: Edward Cree <ecree@solarflare.com> Signed-off-by: David S. Miller <davem@davemloft.net>