eigrpd: Cleanup memory issues on shutdown

eigrpd: Cleanup memory issues on shutdown

a) EIGRP was having issues with the prefix created as part
of the topology destination.  Make this just a part of the
topology data structure instead of allocating it.

b) EIGRP was not freeing up any memory associated with
the network table.  Free it.

c) EIGRP was confusing zebra shutdown as part of the deletion
of the last eigrp data structure.  This was inappropriate it
should be part of the `I'm just shutting down`.

d) The QOBJ was not being properly freed, free it.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>