CoDel is a parameterless queue discipline that handles variable bandwidth
and RTT.

It can be used as the single queue discipline on an interface or as a sub
discipline of existing queue disciplines such as PRIQ, CBQ, HFSC, FAIRQ.

Differential Revision:	https://reviews.freebsd.org/D3272
Reviewd by:	rpaulo, gnn (previous version)
Obtained from:	pfSense
Sponsored by:	Rubicon Communications (Netgate)