dhcp: remove leases when they are released

Don't lock around the Stop() operation though, as that may take
a while and block other operations.  That may mean we call Stop()
multiple times, but the Lease object should handle that correctly
itself.

plugins/ipam/dhcp/daemon.go

@@ -93,6 +93,7 @@ func (d *DHCP) Release(args *skel.CmdArgs, reply *struct{}) error {
 
 	if l := d.getLease(args.ContainerID, conf.Name); l != nil {
 		l.Stop()
+		d.clearLease(args.ContainerID, conf.Name)
 	}
 
 	return nil
@@ -118,6 +119,14 @@ func (d *DHCP) setLease(contID, netName string, l *DHCPLease) {
 	d.leases[contID+netName] = l
 }
 
+func (d *DHCP) clearLease(contID, netName string) {
+	d.mux.Lock()
+	defer d.mux.Unlock()
+
+	// TODO(eyakubovich): hash it to avoid collisions
+	delete(d.leases, contID+netName)
+}
+
 func getListener() (net.Listener, error) {
 	l, err := activation.Listeners(true)
 	if err != nil {