libnetwork: processEndpointDelete: Fix deadlock between getSvcRecords and processEndpointDelete

We had some hosts with quite a bit of cycling containers that ocassionally causes docker daemons to lock up.
Most prominently `docker run` commands do not respond and nothing happens anymore.

Looking at the stack trace the following is at least likely sometimes a cause to that:
Two goroutines g0 and g1 can race against each other:
* (g0) 1. getSvcRecords is called and calls (*network).Lock()
       --> Network is locked.
* (g1) 2. processEndpointDelete is called, and calls (*controller).Lock()
       --> Controller is locked
* (g1) 3. processEndpointDelete tries (*network).ID() which calls (*network).Lock().
* (g0) 4. getSvcRecords calls (*controller).Lock().

3./4. are deadlocked against each other since the other goroutine holds the lock they need.

References b5dc370370/network.go

Signed-off-by: Steffen Butzer <steffen.butzer@outlook.com>

libnetwork/store.go

@@ -399,11 +399,14 @@ func (c *controller) processEndpointDelete(nmap map[string]*netWatch, ep *endpoi
 		return
 	}
 
+	networkID := n.ID()
+	endpointID := ep.ID()
+
 	c.Lock()
-	nw, ok := nmap[n.ID()]
+	nw, ok := nmap[networkID]
 
 	if ok {
-		delete(nw.localEps, ep.ID())
+		delete(nw.localEps, endpointID)
 		c.Unlock()
 
 		// Update the svc db about local endpoint leave right away
@@ -417,9 +420,9 @@ func (c *controller) processEndpointDelete(nmap map[string]*netWatch, ep *endpoi
 
 			// This is the last container going away for the network. Destroy
 			// this network's svc db entry
-			delete(c.svcRecords, n.ID())
+			delete(c.svcRecords, networkID)
 
-			delete(nmap, n.ID())
+			delete(nmap, networkID)
 		}
 	}
 	c.Unlock()