Merge branch 'ethtool_gert_phy_stats-fixes'

Daniil Tatianin says:

====================
net/ethtool/ioctl: split ethtool_get_phy_stats into multiple helpers

This series fixes a potential NULL dereference in ethtool_get_phy_stats
while also attempting to refactor/split said function into multiple
helpers so that it's easier to reason about what's going on.

I've taken Andrew Lunn's suggestions on the previous version of this
patch and added a bit of my own.

Changes since v1:
- Remove an extra newline in the first patch
- Move WARN_ON_ONCE into the if check as it already returns the
  result of the comparison
- Actually split ethtool_get_phy_stats instead of attempting to
  refactor it
====================

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