This change updates the link flow control configuration so that we
correctly set the link flow control settings for DCB.  Previously we would
have to call the fc_enable call 8 times, once for each packet buffer.  If
we move that logic into the fc_enable call itself we can avoid multiple
unnecessary register writes.

This change also corrects an issue in which we were only shifting the water
marks for 82599 parts by 6 instead of 10.  This was resulting in us only
using 1/16 of the packet buffer when flow control was enabled.
Signed-off-by: NAlexander Duyck <alexander.h.duyck@intel.com>
Tested-by: NRoss Brattain <ross.b.brattain@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>