Constant cjdns_ann::LINK_STATE_SLOTS

pub const LINK_STATE_SLOTS: u8 = 18;

Samples are collected every 10 seconds, normally messages are submitted to the Route Server every minute, resulting in 6 samples. But we would store 3 times more samples so that if there is some reason it is unable to submit a message to the route server for up to 3 minutes, still no link state samples will be lost.