ixbge: Make ethtool code account for media types

The i82598 can support various media types but this ethtool
code only was coded for fiber just yet.

Signed-off-by: Ayyappan Veeraiyan <ayyappan.veeraiyan@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>