r8169: remove fiddling with the PCIe max read request size

The attempt to improve performance by changing the PCIe max read request
size was added in the vendor driver more than 10 years back and copied
to r8169 driver. In the vendor driver this has been removed long ago.
Obviously it had no effect, also in my tests I didn't see any
difference. Typically the max payload size is less than 512 bytes
anyway, and the PCI core takes care that the maximum supported value
is set. So let's remove fiddling with PCIe max read request size from
r8169 too.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>