ice: Fix PTP NULL pointer dereference during VSI rebuild

ice: Fix PTP NULL pointer dereference during VSI rebuild

Fix race condition where PTP periodic work runs while VSI is being
rebuilt, accessing NULL vsi->rx_rings.

The sequence was:
1. ice_ptp_prepare_for_reset() cancels PTP work
2. ice_ptp_rebuild() immediately queues PTP work
3. VSI rebuild happens AFTER ice_ptp_rebuild()
4. PTP work runs and accesses NULL vsi->rx_rings

Fix: Keep PTP work cancelled during rebuild, only queue it after
VSI rebuild completes in ice_rebuild().

Added ice_ptp_queue_work() helper function to encapsulate the logic
for queuing PTP work, ensuring it's only queued when PTP is supported
and the state is ICE_PTP_READY.

Error log:
[  121.392544] ice 0000:60:00.1: PTP reset successful
[  121.392692] BUG: kernel NULL pointer dereference, address: 0000000000000000
[  121.392712] #PF: supervisor read access in kernel mode
[  121.392720] #PF: error_code(0x0000) - not-present page
[  121.392727] PGD 0
[  121.392734] Oops: Oops: 0000 [#1] SMP NOPTI
[  121.392746] CPU: 8 UID: 0 PID: 1005 Comm: ice-ptp-0000:60 Tainted: G S                  6.19.0-rc6+ #4 PREEMPT(voluntary)
[  121.392761] Tainted: [S]=CPU_OUT_OF_SPEC
[  121.392773] RIP: 0010:ice_ptp_update_cached_phctime+0xbf/0x150 [ice]
[  121.393042] Call Trace:
[  121.393047]  <TASK>
[  121.393055]  ice_ptp_periodic_work+0x69/0x180 [ice]
[  121.393202]  kthread_worker_fn+0xa2/0x260
[  121.393216]  ? __pfx_ice_ptp_periodic_work+0x10/0x10 [ice]
[  121.393359]  ? __pfx_kthread_worker_fn+0x10/0x10
[  121.393371]  kthread+0x10d/0x230
[  121.393382]  ? __pfx_kthread+0x10/0x10
[  121.393393]  ret_from_fork+0x273/0x2b0
[  121.393407]  ? __pfx_kthread+0x10/0x10
[  121.393417]  ret_from_fork_asm+0x1a/0x30
[  121.393432]  </TASK>

Fixes: 803bef817807d ("ice: factor out ice_ptp_rebuild_owner()")
Signed-off-by: Aaron Ma <aaron.ma@canonical.com>
Tested-by: Sunitha Mekala <sunithax.d.mekala@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>