Merge branch 'ptp-make-virtual-clock-sampling-and-teardown-failure-safe'

James Hilliard says:

====================
ptp: make virtual clock sampling and teardown failure-safe

Fix virtual-clock sampling errors, registration rollback and parent
teardown in separate patches. Keep failed PHC reads out of the timecounter
and serialize extended samples with virtual-clock adjustments. Also
preserve the zero sentinel for packets without hardware timestamps.

Retain the existing cyclecounter mask, scaling and conversion windows.
Retry the first failed refresh promptly, then back off consecutive failures
while preserving regular two-second refresh attempts. Queue the first
refresh immediately after registration. Prolonged sampling gaps remain
subject to the existing half-wrap conversion window and full-wrap sampling
limit.
====================

Link: https://patch.msgid.link/20261026-ptp-vclock-sampling-v6-0-e705612541f1@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>