Userspace proxy should remove conntrack entries

This changes the userspace proxy so that it cleans up its conntrack
settings when a service is removed (as the iptables proxy already
does).  This could theoretically cause problems when a UDP service
as deleted and recreated quickly (with the same IP address).  As
long as packets from the same UDP source IP and port were going to
the same destination IP and port, the the conntrack would apply and
the packets would be sent to the old destination.

This is astronomically unlikely if you did not specify the IP address
to use in the service, and even then, only happens with an "established"
UDP connection.  However, in cases where a service could be "switched"
between using the iptables proxy and the userspace proxy, this case
becomes much more frequent.

cmd/kube-proxy/app/server.go

@@ -272,6 +272,7 @@ func NewProxyServerDefault(config *options.ProxyServerConfig) (*ProxyServer, err
 				loadBalancer,
 				net.ParseIP(config.BindAddress),
 				iptInterface,
+				execer,
 				*utilnet.ParsePortRangeOrDie(config.PortRange),
 				config.IPTablesSyncPeriod.Duration,
 				config.IPTablesMinSyncPeriod.Duration,