Xilinx: ARM: Correct DT 576001 - zero descriptor tracking memory at initialization.

Xilinx: ARM: Correct DT 576001 - zero descriptor tracking memory at initialization.

When the kernel attempts IP address assignment at bootup it closed the interface
without it having ever been opened.  Some cleanup code which expected only NULL
or valid addresses didn't cope with this situation.

Zero descriptor tracking array at initialization to avoid this problem.