Updated fallback seed nodes from sipa's DNS seeds

Fixes issue #3534

Tested by removing peers.dat, then running -listen=0 -dnsseed=0 and verifying that connection happens reasonably quickly and I get:

    Adding fixed seed nodes as DNS doesn't seem to be available.
    Added 600 addresses from 127.0.0.1: 0 tried, 600 new

... in debug.log.