net: mscc: ocelot: extract ocelot_xmit_timestamp() helper

net: mscc: ocelot: extract ocelot_xmit_timestamp() helper

Extract the PTP timestamp handling logic from ocelot_port_xmit() into a
separate ocelot_xmit_timestamp() helper function. This is a pure
refactor with no behavioral change.

The helper returns false if the skb was consumed (freed) due to a
timestamp request failure, and true if the caller should continue with
frame injection. The rew_op value is returned via pointer.

This prepares for splitting ocelot_port_xmit() into separate FDMA and
register injection paths in a subsequent patch.

Signed-off-by: Ziyi Guo <n7l8m4@u.northwestern.edu>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20260208225602.1339325-2-n7l8m4@u.northwestern.edu
Signed-off-by: Jakub Kicinski <kuba@kernel.org>