Distant QRTR nodes can be accessed via an other node that acts as
a bridge. When the a QRTR endpoint associated to a bridge node is
released, all the linked distant nodes should also be released.

This patch fixes endpoint release by:
- Submitting QRTR BYE message locally on behalf of all the nodes
accessible through the endpoint.
- Removing all the routable node IDs from radix tree pointing to
the released node endpoint.
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>