apply erik quanstros tcp-bdp patch (from sources)

this patch consists of two bits of work submitted as one
patch.

the first bit fixed a "pacing" problem, where a tcp connection
rate-limited by the reading process would experience 10%
of the expected throughput, and could even get into live
lock.  it was noticed at the time of this initial work that
the stack often sent tiny grams.  some good bits from nix'
original tcp were merged in.  the test program
	/n/sources/contrib/quanstro/tcptest.c
will verify that under most conditions, a reader-paced connection
now gets the expected throughput.  expected arguments
would be
	tcptest -s1 -n 5000 -l

the second bit is a first step in preparing tcp to handle
modest (1-2MB) bandwidth-delay products.  the strategy
was to completely implement NewReno.  the testing network
was a 7/35/70ms by 100Mbit wan emulator with 0/.05/.1% loss.
here are the performance comparisons from the changes after
the first round "old" to the submitted patch "new".  the
smallest improvement was 80%, the largest was 11x.

loss%	rtt	old	new
0.10	7	4.40	7.85
0.10	35	0.88	1.79
0.10	70	0.47	0.84
0.05	7	4.80	9.38
0.05	35	1.00	2.02
0.05	70	0.52	1.77
0.01	7	5.33	11.87
0.01	35	1.14	10.97
0.01	70	0.54	4.75
0.00	7	4.49	11.92
0.00	35	1.04	11.35
0.00	70	0.58	10.56

since the diff is not very easy to read, i wrote a small
paper detailing the changes

	http://www.quanstro.net/plan9/tcp/tcp.pdf

- erik

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