Replacing the bubble sort with insertion sort gives an 80% reduction
in runtime on average, with randomized keys, for small partitions.

If the keys are pre-sorted, insertion sort runs in linear time, and
even if the keys are reversed, insertion sort is faster than bubble
sort, although not by much.

Update comment describing "tcp_lro_sort()" while at it.

Differential Revision:	https://reviews.freebsd.org/D6619
Sponsored by:	Mellanox Technologies
Tested by:	Netflix
Suggested by:	Pieter de Goeje <pieter@degoeje.nl>
Reviewed by:	ed, gallatin, gnn, transport