ixgbe: fix bit mask for DCB version

This bit mask is wrong DCBX_HOST is always set. It was missed up
until now because lldpad reprograms the device on a link
event. However this is still wrong and it is best not to be
mis-configured for some time immediately following ixgbe_up().

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>