e1000: e1000_ethertool.c coding style fixes

Fixed many errors/warnings and checks in e1000_ethtool.c reported
by checkpatch.pl.  Suggestions from Joe Perches and Alexander Duyck
applied as well
Signed-off-by: Krzysztof Majzerowicz-Jaszcz <cristos@vipserv.org>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>