[Cake] NLA_F_NESTED is missing

[Dean Scarff]

 Hi,

 I've been happily running the out-of-tree sch_cake on my Raspberry Pi 
 since 2015.  However, I recently upgraded my kernel (to 5.4.72 from 
 Raspbian's raspberrypi-kernel 1.20201022-1), which comes with the 
 sch_cake in mainline.  Now, when running:

   sudo /sbin/tc qdisc add dev ppp0 root cake

 I get the error:

   Error: NLA_F_NESTED is missing.

 I get this error with the sch_cake in mainline, and also with sch_cake 
 built out-of-tree.  I also get the error with both Debian's iproute2 
 5.9.0-1 (built myself via debian/rules) and "tc" from dtaht's tc-adv 
 repo.

 Any ideas on what this error means and how to fix it?