igb: report unsupported ethtool settings in set_coalesce

igb: report unsupported ethtool settings in set_coalesce

Orabug: 21792102

There are many settings possible using ethtool -C/--coalesce, but not
all of them are supported in igb. Report failure when an unsupported
option is set.

Signed-off-by: Todd Fujinaka <todd.fujinaka@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit 0c5bbeb8839172990e3b8aa82ae3c166e85a09bc)
Signed-off-by: Brian Maly <brian.maly@oracle.com>