i40e(vf): remove i40e_ethtool_stats.h header file

i40e(vf): remove i40e_ethtool_stats.h header file

Essentially reverts commit 8fd75c58a09a ("i40e: move ethtool
stats boiler plate code to i40e_ethtool_stats.h", 2018-08-30), and
additionally moves the similar code in i40evf into i40evf_ethtool.c.

The code was intially moved from i40e_ethtool.c into i40e_ethtool_stats.h
as a way of better logically organizing the code. This has two problems.
First, we can't have an inline function with variadic arguments on all
platforms. Second, it gave the appearance that we had plans to share
code between the i40e and i40evf drivers, due to having a near copy of
the contents in the i40evf/i40e_ethtool_stats.h file.

Patches which actually attempt to combine or share code between the i40e
and i40evf drivers have not materialized, and are likely a ways off.

Rather than fixing the one function which causes build issues, just move
this code back into the i40e_ethtool.c and i40evf_ethtool.c files. Note
that we also change these functions back from static inlines to just
statics, since they're no longer in a header file.

We can revisit this if/when work is done to actually attempt to share
code between drivers. Alternatively, this stats code could be made more
generic so that it can be shared across drivers as part of ethtool
kernel work.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>