zebra: fix cleanup of meta queues on vrf disable

zebra: fix cleanup of meta queues on vrf disable

Current code treats all metaqueues as lists of route_node structures.
However, some queues contain other structures that need to be cleaned up
differently. Casting the elements of those queues to struct route_node
and dereferencing them leads to a crash. The crash may be seen when
executing bgp_multi_vrf_topo2.

Fix the code by using the proper list element types.

Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>