net: macb: Preserve timestamp settings on rejected requests

gem_set_hwtst() can reject a request after changing the TX one-step
setting, because it programs the TX mode before checking the RX
filter. The call returns -ERANGE, but the hardware may no longer match
the cached configuration.

Validate both settings first and keep the adjusted RX filter local
until validation succeeds. Then apply the register settings and update
the configuration. A rejected request now leaves the hardware, the
caller's settings and the cached configuration unchanged.

Protect the NCR read-modify-write with bp->lock, keeping the descriptor
writes and cache update in the same section. With the register writes
now in the setter, remove gem_ptp_set_one_step_sync() and
gem_ptp_set_ts_mode().

Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>
Reviewed-by: Théo Lebrun <theo.lebrun@bootlin.com>
Tested-by: Nicolai Buchwitz <nb@tipi-net.de>
Signed-off-by: Kim Wooseok <5mghybrid@khu.ac.kr>
Link: https://patch.msgid.link/20260923-macb-hwtstamp-rework-v2-1-75c909b2676d@khu.ac.kr
Signed-off-by: Jakub Kicinski <kuba@kernel.org>