All node_get_all_orports() does is allocate and return a smartlist
with at most two tor_addr_port_t members that match ORPort's of
node configuration. This is harmful for memory efficiency, as it
allocates the same stuff every time it is called. However,
node_is_a_configured_bridge() does not need to call it, as it
already has all the information to check if there is configured
bridge for a given node.
The new code is arranged in a way that hopefully makes each succeeding
linear search through bridge_list less likely.
