igc: fix page fault in XDP TX timestamps handling

igc: fix page fault in XDP TX timestamps handling

If an XDP application that requested TX timestamping is shutting down
while the link of the interface in use is still up the following kernel
splat is reported:

[  883.803618] [   T1554] BUG: unable to handle page fault for address: ffffcfb6200fd008
...
[  883.803650] [   T1554] Call Trace:
[  883.803652] [   T1554]  <TASK>
[  883.803654] [   T1554]  igc_ptp_tx_tstamp_event+0xdf/0x160 [igc]
[  883.803660] [   T1554]  igc_tsync_interrupt+0x2d5/0x300 [igc]
...

During shutdown of the TX ring the xsk_meta pointers are left behind, so
that the IRQ handler is trying to touch them.

This issue is now being fixed by cleaning up the stale xsk meta data on
TX shutdown. TX timestamps on other queues remain unaffected.

Fixes: 15fd021bc427 ("igc: Add Tx hardware timestamp request for AF_XDP zero-copy packet")
Signed-off-by: Zdenek Bouska <zdenek.bouska@siemens.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-by: Florian Bezdeka <florian.bezdeka@siemens.com>
Tested-by: Avigail Dahan <avigailx.dahan@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>