net: ravb: Fix max TX frame size for RZ/V2M

When tx_max_frame_size was added to struct ravb_hw_info, no value was
set in ravb_rzv2m_hw_info so the default value of zero was used.

The maximum MTU is set by subtracting from tx_max_frame_size to allow
space for headers and frame checksums. As ndev->max_mtu is unsigned,
this subtraction wraps around leading to a ridiculously large positive
value that is obviously incorrect.

Before tx_max_frame_size was introduced, the maximum MTU was based on
rx_max_frame_size. So, we can restore the correct maximum MTU by copying
the rx_max_frame_size value into tx_max_frame_size for RZ/V2M.

Fixes: 1d638642 ("net: ravb: Fix maximum TX frame size for GbEth devices")
Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Link: https://patch.msgid.link/20250109113706.1409149-1-paul.barker.ct@bp.renesas.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>