igb: cleanup igb.h header whitespace and some structure formatting

This patch changes the layout of the ring and adapter structs to fill a few
holes in the structure.  It also cleans up some whitespace and formatting
issues.

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>