ixgb: use DPRINTK and msglvl, and ethtool to control it

Use DPRINTK and msglvl, and ethtool to control it. Add proper names
to netdev structs and mappings.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: John Ronciak <john.ronciak@intel.com>