ixgbe: Do not disable read relaxed ordering when DCA is enabled

ixgbe: Do not disable read relaxed ordering when DCA is enabled

A previous fix had gone though and disabled relaxed ordering for Rx
descriptor read fetching.  This was not necessary as this functions
correctly and has no ill effects on the system.

In addition several of the defines used for the DCA control registers were
incorrect in that they indicated descriptor effects when they actually had
an impact on either data or header write back.  As such I have update these
to correctly reflect either DATA or HEAD.

(cherry picked from commit bdda1a61c1dbb1e3a4f76c944b7c1e3b3731c861)
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Stephen Ko <stephen.s.ko@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Joe Jin <joe.jin@oracle.com>