vxge: Add const to ethtool_driver_stats_keys

Move about half a KB of data to text.

Miscellanea:

o Move strings out of the .h file into the .c file
  in case the .h file is ever #included twice

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>