realtek: eth: be defensive in rteth_confirm_and_disable_irqs()

realtek: eth: be defensive in rteth_confirm_and_disable_irqs()

With latest refactoring irq activation and deactivation is side-by-side
in the code. This makes it easier to align these functions. Current
assumption is, that the ethernet irq is only called on one cpu and
napi handling does not interfere. So it should be totally fine to
run irq disabling (called from interrupt handler) without locks.
Nevertheless be defensive and add a lock(). So in the case the ethernet
irq is fired twice on two cpus (e.g. RTL931x) the code is on the
safe side.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/22156
Signed-off-by: Robert Marko <robimarko@gmail.com>