doc: announce ABI changes for new flow director modes

doc: announce ABI changes for new flow director modes

For x550 supports 2 new flow director modes, MAC VLAN and Cloud.
The MAC VLAN mode means the MAC and VLAN are monitored.
The Cloud mode is for VxLAN and NVGRE, and the tunnel type,
TNI/VNI, inner MAC and inner VLAN are monitored.
So, there're a few new lookup fields for these 2 new modes, like MAC,
tunnel type, TNI/VNI.
We have to change the ABI to support these new lookup fields.

Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>