ice: restore PTP Rx timestamp config after ethtool set-channels

When ethtool -L changes queue counts, ice_vsi_recfg_qs() closes and
rebuilds the VSI, reallocating Rx rings. The newly allocated rings have
ptp_rx cleared, so RX hardware timestamps are no longer attached to skb
until hwtstamp configuration is applied again.

Restore timestamp mode after ice_vsi_open() in the queue reconfiguration
path, matching reset/rebuild behavior and ensuring newly rebuilt Rx rings
have PTP RX timestamping re-enabled.

Testing hints:
- run ptp4l application in client synchronization mode:
	 ptp4l -i ethX -m -s
- run PTP traffic
- change queue number on ethX netdev interface:
	ethtool -L ethX combined new_queue_size
- observe ptp4l output
- expected result: no "received DELAY_REQ without timestamp" messages

Fixes: 77a781155a ("ice: enable receive hardware timestamping")
Cc: stable@vger.kernel.org
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Grzegorz Nitka <grzegorz.nitka@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Alexander Nowlin <alexander.nowlin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://patch.msgid.link/20260515182419.1597859-7-anthony.l.nguyen@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/intel/ice/ice_main.c

@@ -4104,6 +4104,12 @@ int ice_vsi_recfg_qs(struct ice_vsi *vsi, int new_rx, int new_tx, bool locked)
 	}
 	ice_pf_dcb_recfg(pf, locked);
 	ice_vsi_open(vsi);
+	/* Rx rings are reallocated during VSI rebuild and lose their ptp_rx
+	 * flag. Restore timestamp mode so newly allocated rings are set up
+	 * for hardware Rx timestamping.
+	 */
+	if (test_bit(ICE_FLAG_PTP_SUPPORTED, pf->flags))
+		ice_ptp_restore_timestamp_mode(pf);
 	goto done;
 
 rebuild_err: