missed the update to calculate prr_out properly
in the case when pipe < ssthresh.

prr_out should account for all packets sent during the
recovery episode. As an approximation (valid under
heavy loss), the original patch only uses
sackhint.sack_bytes_rexmit. This misses all packets
sent beyond recovery Point (snd_recover).

For the pipe > ssthresh case, this was fixed in D28941