igb: remove media type fiber as it is misleading

The current igb driver only supports copper and serdes.  The fiber media
type is a holdover from earlier NICs as the current nics supported by igb
all use serdes when communicating over a fiber connection.  As a result we
can remove media type fiber without losing any functionality.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>