Afternoon (well it is for me)

I seem to remember a recent request to be able to specify the codel
interval parameter within cake.  I've just pushed a branch
'exposeinterval' to both sch_cake & tc-adv which I believe does this.

My coding is very much of the copy'n'paste'n'tweak level so this
definitely needs looking over by skilled & experienced eyes, however in
the spirit of collaboration it might be a start.

Another warning: Nothing has been tested; sch-cake compiles.  tc-adv
hasn't even been tested that far yet!  Hopefully this evening will
rectify that as I'll be able to give the kiss of life to my router if
needed :-)

Maybe useful, maybe not. push/pull/tweak/delete as seen fit