[lwip-users] tcp lost ack bug

[Jani Monoses]

Hi
there's a bug causing the connection to hang when
a single ack (not piggybacked) is lost when transmitted from lwip.
When it's part of a data segment it's OK because those are retransmitted
but single acks are not.

in tcp_receive there's a test for duplicate segments (those which have already
been received and acked once) and no action is taken on receipt of such a 
segment
they need to be acked too - that's the single path in receive where no ack is 
sent
at all.Otherwise lwip keeps discarding them because they've been acked but the 
ack
never went through and the peer keeps sending the segment.
I commited a fix but comments are welcome
Jani