ixgbevf: Add zero_base handler to network statistics

This patch removes the need to keep a zero_base variable in the adapter
structure. Now we just use two different macros to set the non-zero and
zero base. This adds to readability and shortens some of the structure
initialization under 80 columns. The gathering of status for ethtool was
slightly modified to again better fit into 80 columns and become a bit
more readable.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>