[ns] Bug report: slowdown() in tcp.cc

["Guo, Liang" <guol@cs.bu.edu>]

in slowdown() function of tcp.cc, when dealing with CLOSE_CWND_HALF
option, it is possible to set 
the value of cwnd_ to be less than 1, which can cause
unnecessary timeouts (when ecn is enabled). This has been pointed out
explicitly in draft-ietf-tsvwg-ecn-03.txt (page 18): 
      "However, the value of the congestion window is bounded
below by a value of one MSS".

So following patch should be applied.

874c958
< 	if (how & CLOSE_CWND_HALF)
---
> 	if (how & CLOSE_CWND_HALF) {
879a964,968
> 
> 		// added by Liang Guo 2001/03/31, cwnd shouldn't be
smaller than 1
> 		if (cwnd_ < 1)
> 			cwnd_ = 1;
> 	}