chore: update go-multiaddr to v0.15

[MarcoPolo]

Updates the go-multiaddr dependency and this Lotus' usage of go-multiaddr. Rationale for this breaking change can be found in the draft release notes of go-multiaddr: https://github.com/multiformats/go-multiaddr/releases/. But the tl;dr is that this breaking change gets us away from the easy-to-misuse Mutliaddr interface that has led to many nil-ptr panics.

Another important thing to note: You'll likely need this patch https://github.com/libp2p/go-libp2p-kad-dht/pull/1046 backported to whatever go-libp2p-kad-dht version you're on if you don't want to update that dependency. Currently this branch points to a commit that is Lotus's current version of kad-dht (v0.25.2) plus that patch.

Requires:

• [ ] https://github.com/libp2p/go-libp2p/pull/3145
• [x] https://github.com/libp2p/go-libp2p-kad-dht/pull/1030 or https://github.com/libp2p/go-libp2p-kad-dht/pull/1046 backported.