Print the nested stats attribute containing timestamping statistics when
the --show-time-stamping flag is used.

  [root@binary-eater-vm-01 linux-ethtool-ts]# ./tools/net/ynl/ethtool.py --show-time-stamping mlx5_1
  Time stamping parameters for mlx5_1:
  Capabilities:
    hardware-transmit
    hardware-receive
    hardware-raw-clock
  PTP Hardware Clock: 0
  Hardware Transmit Timestamp Modes:
    off
    on
  Hardware Receive Filter Modes:
    none
    all
  Statistics:
    tx-pkts: 8
    tx-lost: 0
    tx-err: 0
Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Link: https://lore.kernel.org/r/20240403212931.128541-8-rrameshbabu@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>