netlink: Use ifindex of parent TC object when searching leaf qdiscs
netlink: Use ifindex of parent TC object when searching leaf qdiscs

The qdisc cache is host wide, the parent classid is not unique
so the ifindex of the parent tc object must be set in the filter
otherwise a leaf qdisc with an identical parent id in another
device can be mistaken.

This also converts the class_cache to be passed up through the
stack to make clear it is not system wide but specific to the
ifindex we are currently handling.

Signed-off-by: Thomas Graf <17c2d8920621522552b392f72d8fdb4d1e866b44@suug.ch>

Chocobo1/bmon,Chocobo1/bmon,tklauser/bmon,tklauser/bmon