Constant libp2p_rendezvous::MIN_TTL

pub const MIN_TTL: Ttl = 60 * 60 * 2; // 0x0000_0000_0000_1c20u64

By default, nodes should require a minimum TTL of 2h

https://github.com/libp2p/specs/tree/master/rendezvous#recommendations-for-rendezvous-points-configurations.