net: tcp: Correctly handle partial duplicate buffered out of order data

TCP is a streaming protocol, this means it can set the packet boundary
at an arbitrary location. Therefor a re-transmitted packet may have the
packet boundary at a different location from the original missing segment.

The reordering logic should be able to deal with this situation and
throw away the overlapping data. Now also for data that needs to be added
to the existing queue

Signed-off-by: Sjors Hettinga <s.a.hettinga@gmail.com>