bug #49631: handle zero-window probe and refused_data

This commit adds support for responding to a zero-window probe when
the refused_data pointer is set

A zero-window probe is a data segment received when rcv_ann_wnd
is 0. This corrects a standards violation where LwIP would not
respond to a zero-window probe with its current ACK value (RCV.NXT)
when it has refused data, thus leading to the probing TCP closing
out the connection
1 file changed