plugin/forward: move Dial goroutine out (#1738)

Rework the TestProxyClose - close the proxy in the *same* goroutine
as where we started it. Close channels as long as we don't get dataraces
(this may need another fix).

Move the Dial goroutine out of the connManager - this simplifies things
*and* makes another goroutine go away and removes the need for connErr
channels - can now just be dns.Conn.

Also:

Revert "plugin/forward: gracefull stop (#1701)"
This reverts commit 135377bf77.

Revert "rework TestProxyClose (#1735)"
This reverts commit 9e8893a0b5.

plugin/forward/connect.go

@@ -34,16 +34,6 @@ func (p *Proxy) updateRtt(newRtt time.Duration) {
 }
 
 func (p *Proxy) connect(ctx context.Context, state request.Request, forceTCP, metric bool) (*dns.Msg, error) {
-	atomic.AddInt32(&p.inProgress, 1)
-	defer func() {
-		if atomic.AddInt32(&p.inProgress, -1) == 0 {
-			p.checkStopTransport()
-		}
-	}()
-	if atomic.LoadUint32(&p.state) != running {
-		return nil, errStopped
-	}
-
 	start := time.Now()
 
 	proto := state.Proto()
@@ -55,6 +45,7 @@ func (p *Proxy) connect(ctx context.Context, state request.Request, forceTCP, me
 	if err != nil {
 		return nil, err
 	}
+
 	// Set buffer size correctly for this client.
 	conn.UDPSize = uint16(state.Size())
 	if conn.UDPSize < 512 {