net/iavf: count continuous DD bits for Arm in flex Rx

net/iavf: count continuous DD bits for Arm in flex Rx

On Arm platforms, reading of descriptors may be re-ordered causing the
status of DD bits to be discontinuous. Add logic to only process
continuous descriptors by checking DD bits.

Fixes: b8b4c54ef9b0 ("net/iavf: support flexible Rx descriptor in normal path")
Cc: stable@dpdk.org
Signed-off-by: Kathleen Capella <kathleen.capella@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Qi Zhang <qi.z.zhang@intel.com>