ospfd: fix cleanup of MaxAge LSAs on exit

ospfd: fix cleanup of MaxAge LSAs on exit

During shutdown, the ospf->maxage_lsa table is iterated over to
clean up all existing entries. While doing that, route_unlock_node()
should be called only for the nodes that have an associated entry,
otherwise the table will get corrupted and ospfd will crash.

As a side note, using a routing table to store MaxAge LSAs was a
very poor choice of a data structure, considering that a simple
rb-tree or hash table would get the job done with a much simpler
(and less error-prone) API. Something to cleanup in the future...

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>