During unidirectional data transmission, a TCP connection may stall.

During unidirectional data transmission, a TCP connection may stall.
The sending machine is doing zero window probes, but is not sending
any more data although the other machine announced that it has space
again.  The header prediction code did not update snd_wl2.  If there
was a sequence number wrap, the send window update block is not
reached.
Update snd_wl2 when receiving predicted ACKs and and update snd_wl1
and rcv_up for predicted pure data.
from FreeBSD; OK sashan@ claudio@