[Cake] Upstream submission of dual-mode fairness patch

[George Amanakis]

I ran some tests with shaping ingress (ifb) and egress on the same
physical interface, albeit without vlans:

IP1, 1 up: 	45.07
IP2, 32 up:	45.06
IP1, 32 down:	45.64 mbit/s
IP2, 1 down:	44.50

This is on x86_64, kernel 4.20.12, iproute 4.20.

qdisc cake 8006: dev enp1s0 root refcnt 2 bandwidth 100Mbit diffserv3
dual-srchost nonat nowash no-ack-filter split-gso nofwmark rtt 100.0ms
noatm overhead 38 mpu
84                                                           

qdisc cake 8002: dev ifb0 root refcnt 2 bandwidth 100Mbit diffserv3
dual-dsthost nonat nowash no-ack-filter split-gso nofwmark rtt 100.0ms
noatm overhead 38 mpu 84 


I will setup a vlan and try again.