Merge branch 'dsa-serdes-stats'

Andrew Lunn says:

====================
Export SERDES stats via ethtool -S

The mv88e6352 family has a SERDES interface which can be used for
example to connect to SFF/SFP modules. This interface has a couple of
statistics counters. Add support for including these counters in the
output of ethtool -S.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>