manager: return most recent connection in active_connection_find()
When a connection is reactivated, there could be two active connections tracked by the manager: the deactivating one and the new one. Ensure that we first return the most recent one so that slaves will pick the right master.
Fixes-test: @iptunnel_gretap_doc_procedure
Fixes: dc6ec6ce ('core: reverse the order of active connections in the manager')