CVE-2026-98791: net/mlx5e: Fix AF_XDP TX timestamp teardown NULL dereference

In the Linux kernel, the following vulnerability has been resolved: net/mlx5e: Fix AF_XDP TX timestamp teardown NULL dereference During XSK TX queue teardown, outstanding descriptors are completed without a CQE. If one requested a TX timestamp, the completion path passes that NULL CQE to mlx5e_xsk_fill_timestamp(), which dereferences it. Return zero when no CQE is available, indicating that teardown did not produce a TX timestamp.