net: Add support for providing the PTP hardware source in tsinfo

net: Add support for providing the PTP hardware source in tsinfo

Multi-PTP source support within a network topology has been merged,
but the hardware timestamp source is not yet exposed to users.
Currently, users only see the PTP index, which does not indicate
whether the timestamp comes from a PHY or a MAC.

Add support for reporting the hwtstamp source using a
hwtstamp-source field, alongside hwtstamp-phyindex, to describe
the origin of the hardware timestamp.

Remove HWTSTAMP_SOURCE_UNSPEC enum value as it is not used at all.

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Link: https://patch.msgid.link/20250519-feature_ptp_source-v4-1-5d10e19a0265@bootlin.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>