Bump libp2p to address inconsistency in mesh peer tracking (#2493)

## Issue Addressed

- Resolves #2457
- Resolves #2443

## Proposed Changes

Target the (presently unreleased) head of `libp2p/rust-libp2p:master` in order to obtain the fix from libp2p/rust-libp2p#2175.

Additionally:

- `libsecp256k1` needed to be upgraded to satisfy the new version of `libp2p`.
- There were also a handful of minor changes to `eth2_libp2p` to suit some interface changes.
- Two `cargo audit --ignore` flags were remove due to libp2p upgrades.

## Additional Info
 
 NA