ixgbe: consolidate, setup for multiple traffic classes

This consolidates setup code for multiple traffic classes in
the setup_tc routine.

Prep work to allow IEEE DCBX to optimize for number of traffic
classes. Also simplifies code paths.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>