Add additional libp2p tests (#1867)

## Issue Addressed

N/A

## Proposed Changes

Adds tests for the eth2_libp2p crate.

beacon_node/eth2_libp2p/src/rpc/protocol.rs

@@ -163,8 +163,8 @@ impl<TSpec: EthSpec> UpgradeInfo for RPCProtocol<TSpec> {
 /// Represents the ssz length bounds for RPC messages.
 #[derive(Debug, PartialEq)]
 pub struct RpcLimits {
-    min: usize,
-    max: usize,
+    pub min: usize,
+    pub max: usize,
 }
 
 impl RpcLimits {