bgpd: Fix route node unlock when clearing adj-out

bgpd: Fix route node unlock when clearing adj-out

When clearing the adj-out for a subgroup (e.g., upon peer going down),
ensure that the adj-out is removed before unlocking the route node that
it points to, otherwise, there is a possibility that the route node may
be prematurely freed.

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Ticket: CM-13690
Reviewed By: None
Testing Done: bgp-smoke, resilient-hash tests

(cherry picked from commit c3d7d35f3b7152c9e50e52c3cfd60b0dc52df703)
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>