p2p: fix yet another disconnect hang

Peer.readLoop will only terminate if the connection is closed. Fix the
hang by closing the connection before waiting for readLoop to terminate.

This also removes the british disconnect procedure where we're waiting
for the remote end to close the connection. I have confirmed with
@subtly that cpp-ethereum doesn't adhere to it either.

p2p/peer.go

@@ -4,7 +4,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net"
 	"sort"
 	"sync"
@@ -21,7 +20,6 @@ const (
 	baseProtocolMaxMsgSize = 10 * 1024 * 1024
 
 	pingInterval = 15 * time.Second
-	disconnectGracePeriod = 2 * time.Second
 )
 
 const (
@@ -129,39 +127,27 @@ func (p *Peer) run() DiscReason {
 	case err := <-readErr:
 		if r, ok := err.(DiscReason); ok {
 			reason = r
-			break
+		} else {
-		}
 			// Note: We rely on protocols to abort if there is a write
 			// error. It might be more robust to handle them here as well.
 			p.DebugDetailf("Read error: %v\n", err)
-		p.conn.Close()
 			reason = DiscNetworkError
+		}
 	case err := <-p.protoErr:
 		reason = discReasonForError(err)
 	case reason = <-p.disc:
 	}
 
 	close(p.closed)
-	p.wg.Wait()
-	if reason != DiscNetworkError {
 	p.politeDisconnect(reason)
-	}
+	p.wg.Wait()
 	p.Debugf("Disconnected: %v\n", reason)
 	return reason
 }
 
 func (p *Peer) politeDisconnect(reason DiscReason) {
-	done := make(chan struct{})
+	if reason != DiscNetworkError {
-	go func() {
 		SendItems(p.rw, discMsg, uint(reason))
-		// Wait for the other side to close the connection.
-		// Discard any data that they send until then.
-		io.Copy(ioutil.Discard, p.conn)
-		close(done)
-	}()
-	select {
-	case <-done:
-	case <-time.After(disconnectGracePeriod):
 	}
 	p.conn.Close()
 }