r330675 introduced an extra window check in the LRO code to ensure it
captured and reported the highest window advertisement with the same
SEQ/ACK. However, the window comparison uses modulo 216 math, rather
than directly comparing the absolute values. Because windows use
absolute values and not modulo 216 math (i.e. they don't wrap), we
need to compare the absolute values.

Reviewed by: gallatin
MFC after: 3 days
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D14937