Free skb->cb usage in core driver and let device drivers decide to
use or not. The reason having a DSA_SKB_CB(skb)->clone was because
dsa_skb_tx_timestamp() which may set the clone pointer was called
before p->xmit() which would use the clone if any, and the device
driver has no way to initialize the clone pointer.

Although for now putting memset(skb->cb, 0, 48) at beginning of
dsa_slave_xmit() by this patch is not very good, there is still way
to improve this. Otherwise, some other new features, like one-step
timestamp which needs a flag of skb marked in dsa_skb_tx_timestamp(),
and handles as one-step timestamp in p->xmit() will face same
situation.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
---
Changes for v2:
	- Added this patch.
---
 drivers/net/dsa/ocelot/felix.c         |  1 +
 drivers/net/dsa/sja1105/sja1105_main.c |  2 +-
 drivers/net/dsa/sja1105/sja1105_ptp.c  |  4 +++-
 drivers/net/ethernet/mscc/ocelot.c     |  6 +++---
 drivers/net/ethernet/mscc/ocelot_net.c |  2 +-
 include/linux/dsa/sja1105.h            |  3 ++-
 include/net/dsa.h                      | 14 --------------
 include/soc/mscc/ocelot.h              |  8 ++++++++
 net/dsa/slave.c                        |  3 +--
 net/dsa/tag_ocelot.c                   |  8 ++++----
 net/dsa/tag_ocelot_8021q.c             |  8 ++++----
 11 files changed, 28 insertions(+), 31 deletions(-)

diff --git a/drivers/net/dsa/ocelot/felix.c b/drivers/net/dsa/ocelot/felix.c
index d679f023dc00..8980d56ee793 100644
--- a/drivers/net/dsa/ocelot/felix.c
+++ b/drivers/net/dsa/ocelot/felix.c

@@ -1403,6 +1403,7 @@ static bool felix_txtstamp(struct dsa_switch *ds, int port,

 	if (ocelot->ptp && ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP) {
 		ocelot_port_add_txtstamp_skb(ocelot, port, clone);
+		OCELOT_SKB_CB(skb)->clone = clone;
 		return true;
 	}