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 https://github.com/libp2p/rust-libp2p/pull/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

beacon_node/eth2_libp2p/src/rpc/handler.rs

@@ -59,6 +59,7 @@ type InboundProcessingOutput<TSpec> = (
 type HandlerEvent<T> = Result<RPCReceived<T>, HandlerErr>;
 
 /// An error encountered by the handler.
+#[derive(Debug)]
 pub enum HandlerErr {
     /// An error occurred for this peer's request. This can occur during protocol negotiation,
     /// message passing, or if the handler identifies that we are sending an error response to the peer.