MFC 220794:

MFC 220794:
When checking to see if a window update should be sent to the remote peer,
don't force a window update if the window would not actually grow due to
window scaling.  Specifically, if the window scaling factor is larger than
2 * MSS, then after the local reader has drained 2 * MSS bytes from the
socket, a window update can end up advertising the same window.  If this
happens, the supposed window update actually ends up being a duplicate ACK.
This can result in an excessive number of duplicate ACKs when using a
higher maximum socket buffer size.

git-svn-id: svn://svn.freebsd.org/base/stable/8@222936 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f