r8169: make use of the unaligned access helpers

Instead of open-coding unaligned access let's use the predefined
unaligned access helpers.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/cfaf9176-e4f9-c32d-4d4d-e8fb52009f35@gmail.com


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