Bit 27 of the RX buffer desc word 1 should be set when the packet was
accepted due to specific address register match. Implement.

This feature is absent from the Xilinx documentation (UG585) but the
behaviour is tested as accurate on real hardware.
Reported-by: NDeepika Dhamija <deepika@xilinx.com>
Signed-off-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 7e3f26fc4ab244e8123efc12723e7164730abdcb.1386136219.git.peter.crosthwaite@xilinx.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>