This fixes several breakages (panics) since the tcp_lro code was
committed that have been reported. Quite a few new features are
now in rack (prefecting of DGP -- Dynamic Goodput Pacing among the
largest). There is also support for ack-war prevention. Documents
comming soon on rack..

Sponsored by:           Netflix
Reviewed by:		rscheff, mtuexen
Differential Revision:	https://reviews.freebsd.org/D30036