r8152: Advertise software timestamp information.

r8152: Advertise software timestamp information.

Driver calls skb_tx_timestamp(skb) in rtl8152_start_xmit(), but does not advertise the capability in ethtool.
Advertise software timestamp capabilities on struct ethtool_ops.

Signed-off-by: Abhishek Rawal <rawal.abhishek92@gmail.com>
Reviewed-by: Jamie Bainbridge <jamie.bainbridge@gmail.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://patch.msgid.link/20251014055234.46527-1-rawal.abhishek92@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>