lldpd: don't call `lldpd_count_neighbors()` too many times
lldpd: count number of chassis to get number of neighbors

Also, if only one neighbor, just display its name.
lldpd: when no `setproctitle()` available, don't count neighbors
debian: build-depends on libbssd-dev
compat: declare `setproctitle()` as a printf function