Attempt Pending Request to BUSY && ASSIGNED && DISCONNECTED Peer

[RatanRSur]

Any process that depends on pre-assigned peer tasks is liable to grow our pendingRequests out of control.

When we attempt to execute a pending transaction, we check for that peers availability:

besu/ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/manager/PendingPeerRequest.java

Lines 62 to 68 in bac5c67

	final Optional<EthPeer> selectedPeer =
	leastBusySuitablePeer.filter(EthPeer::hasAvailableRequestCapacity);
	selectedPeer.ifPresent(this::sendRequest);
	return selectedPeer.isPresent();
	}
	}

However, if that peer was disconnected while there were max outstanding requsts, we'll never reattempt it as selectedPeer will be empty. Furthermore, we'll return false and keep that pending request in our list of requests.

With this change we indicate that we aren't waiting for any outstanding requests when we disconnect from a peer, allowing the existing logic that triggers when peers are disconnected to be hit.

The getter I added just for testing purposes was to get around the inadequecies of the MockPeerConnection. There's a whole lot of callback plumbing that's needed for a simple ethPeer.disconnect to do the same thing it does when we call it in our production code.