net/mlx5e: Implement AF_XDP TX timestamp and checksum offload

net/mlx5e: Implement AF_XDP TX timestamp and checksum offload

TX timestamp:
- requires passing clock, not sure I'm passing the correct one (from
  cq->mdev), but the timestamp value looks convincing

TX checksum:
- looks like device does packet parsing (and doesn't accept custom
  start/offset), so I'm ignoring user offsets

Cc: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20231127190319.1190813-5-sdf@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>