net: dlink: add synchronization for stats update

This patch synchronizes code that accesses from both user-space
and IRQ contexts. The `get_stats()` function can be called from both
context.

`dev->stats.tx_errors` and `dev->stats.collisions` are also updated
in the `tx_errors()` function. Therefore, these fields must also be
protected by synchronized.

There is no code that accessses `dev->stats.tx_errors` between the
previous and updated lines, so the updating point can be moved.

Signed-off-by: Moon Yeounsu <yyyynoom@gmail.com>
Link: https://patch.msgid.link/20250515075333.48290-1-yyyynoom@gmail.com


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