The RTL8221B PHY is a newer version of the RTL8226, also supporting
2.5GBit Ethernet. It is found with RTL931X devices such as the
EdgeCore ECS4125-10P
Signed-off-by: Sebastian Gottschall <s.gottschall@dd-wrt.com>
Signed-off-by: Birger Koblitz <git@birger-koblitz.de>