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