SACK broken in HEAD/RELENG_7

[Mike Silbersack]

On Mon, 26 Nov 2007, James Healy wrote:

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> While monitoring a data transfer between two 7-beta3 hosts with tcpdump
> and SIFTR[1] last week, we noticed that SACK was not being negotiated as
> expected.

> James Healy and Lawrence Stewart

Good detective work!

I'll get this change commited in the next day or two.

-Mike