tcp: Rack compressed ack path updates the recv window too easily

The compressed ack path of rack is not following proper procedures in updating
the peers window. It should be checking the seq and ack values before updating and
instead it is blindly updating the values. This could in theory get the wrong window
in the connection for some length of time.

Reviewed by: tuexen
Sponsored by: Netflix Inc.
Differential Revision: https://reviews.freebsd.org/D32082