ixgbe: consolidate packet buffer allocation

ixgbe: consolidate packet buffer allocation

Consolidate packet buffer allocation currently being
done in the DCB path and main path. This allows the
feature set and packet buffer requirements to be done
once.

This is prep work to allow DCB to coexist with other
features namely, flow director.

CC: Alexander Duyck <alexander.h.duyck@intel.com>
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>
(cherry picked from commit 80605c6513207344d00b32e8d1e64bd34fdf1358)

Signed-off-by: Joe Jin <joe.jin@oracle.com>