Make addrman's bucket placement deterministic.

Give each address a single fixed location in the new and tried tables,
which become simple fixed-size arrays instead of sets and vectors.

This prevents attackers from having an advantages by inserting an
address multiple times.

This change was suggested as Countermeasure 1 in
Eclipse Attacks on Bitcoin’s Peer-to-Peer Network, Ethan Heilman,
Alison Kendler, Aviv Zohar, Sharon Goldberg. ePrint Archive Report
2015/263. March 2015.

It is also more efficient.