ixgbe: cleanup copyright string for 2011

Updating the copyrights for 2011 as well as make the ixgbe_copyright string
a constant.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Stephen Ko <stephen.s.ko@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>