Merge branch 'provide-KAPI-for-SQI'

Oleksij Rempel says:

====================
provide KAPI for SQI

This patches are extending ethtool netlink interface to export Signal
Quality Index (SQI). SQI provided by 100Base-T1 PHYs and can be used for
cable diagnostic. Compared to a typical cable tests, this value can be
only used after link is established.

changes v3:
- rename __ethtool_get_sqi* to linkstate_get_sqi*. And move this
  functions to the net/ethtool/linkstate.c
- protect linkstate_get_sqi* with locking

changes v2:
- use u32 instead of u8 for SQI
- add SQI_MAX field and callbacks
- some style fixes in the rst.
- do not convert index to shifted index.
====================

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