eth: unregister peer only when handler exits (#22908)

This removes the error log message that says 

    Ethereum peer removal failed ... err="peer not registered"

The error happened because removePeer was called multiple
times: once to disconnect the peer, and another time when the
handler exited. With this change, removePeer now has the sole
purpose of disconnecting the peer. Unregistering happens exactly
once, when the handler exits.

p2p/peer.go

@@ -115,7 +115,8 @@ type Peer struct {
 	disc     chan DiscReason
 
 	// events receives message send / receive events if set
-	events *event.Feed
+	events   *event.Feed
+	testPipe *MsgPipeRW // for testing
 }
 
 // NewPeer returns a peer for testing purposes.
@@ -128,6 +129,15 @@ func NewPeer(id enode.ID, name string, caps []Cap) *Peer {
 	return peer
 }
 
+// NewPeerPipe creates a peer for testing purposes.
+// The message pipe given as the last parameter is closed when
+// Disconnect is called on the peer.
+func NewPeerPipe(id enode.ID, name string, caps []Cap, pipe *MsgPipeRW) *Peer {
+	p := NewPeer(id, name, caps)
+	p.testPipe = pipe
+	return p
+}
+
 // ID returns the node's public key.
 func (p *Peer) ID() enode.ID {
 	return p.rw.node.ID()
@@ -185,6 +195,10 @@ func (p *Peer) LocalAddr() net.Addr {
 // Disconnect terminates the peer connection with the given reason.
 // It returns immediately and does not wait until the connection is closed.
 func (p *Peer) Disconnect(reason DiscReason) {
+	if p.testPipe != nil {
+		p.testPipe.Close()
+	}
+
 	select {
 	case p.disc <- reason:
 	case <-p.closed: