DCTCP (Data Center TCP) implementation.

DCTCP congestion control algorithm aims to maximise throughput and minimise
latency in data center networks by utilising the proportion of Explicit
Congestion Notification (ECN) marked packets received from capable hardware as a
congestion signal.

Highlights:
Implemented as a mod_cc(4) module.
ECN (Explicit congestion notification) processing is done differently from
RFC3168.
Takes one-sided DCTCP into consideration where only one of the sides is using
DCTCP and other is using standard ECN.

IETF draft: http://tools.ietf.org/html/draft-bensley-tcpm-dctcp-00
Thesis report by Midori Kato: https://eggert.org/students/kato-thesis.pdf

Submitted by: Midori Kato <katoon@sfc.wide.ad.jp> and

		Lars Eggert <lars@netapp.com>
		with help and modifications from
		hiren

Differential Revision: https://reviews.freebsd.org/D604
Reviewed by: gnn