net: cpsw: ti: Reap completed packets before stopping interface

net: cpsw: ti: Reap completed packets before stopping interface

If you send a final packet just before stopping the interface (e.g. a final
ACK as part of the UDP fastboot protocol), then that packet isn't reliably
delivered onto the wire.

Reap packets prior to stopping the interface to ensure any which are
in-flight make it out. Also remove buffer and len from the call to
cpdma_process() as we weren't using them on their return.

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>