try harder to minimize MPR count
each time we hear about a new route to a 2-hop neighbor, see if it's a previously selected MPR and use it instead
introduce extend_route_validity
so we don't try to attempt costly operations for routes we already know
reorder struct entries for better alignment
re-add hop count to free_node
it's only used to keep the list someway sorted, for fewer iterations
Without it, simple_list_add_before will crash (how did it even work until now?!)
abort early when last_addr == NULL
refactor add_olsr_node
silence warnings
make private functions static
remove unused functions
use a bit field for 'bool' properties of olsr_node to save memory