igb: don't break user visible strings over multiple lines in igb_ethtool.c

Even when they go beyond 80 characters, user visible strings should be
on one line to make them easy to grep for.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>