Plumb the conntrack.Interface up to the proxiers

And use the fake interface in the unit tests, removing the dependency
on setting up FakeExec stuff when conntrack cleanup will be invoked.

Also, remove the isIPv6 argument to CleanStaleEntries, because it can
be inferred from the other args.

pkg/proxy/iptables/proxier.go

@@ -170,7 +170,7 @@ type Proxier struct {
 	iptables       utiliptables.Interface
 	masqueradeAll  bool
 	masqueradeMark string
-	exec           utilexec.Interface
+	conntrack      conntrack.Interface
 	localDetector  proxyutiliptables.LocalTrafficDetector
 	hostname       string
 	nodeIP         net.IP
@@ -283,7 +283,7 @@ func NewProxier(ipFamily v1.IPFamily,
 		iptables:                 ipt,
 		masqueradeAll:            masqueradeAll,
 		masqueradeMark:           masqueradeMark,
-		exec:                     exec,
+		conntrack:                conntrack.NewExec(exec),
 		localDetector:            localDetector,
 		hostname:                 hostname,
 		nodeIP:                   nodeIP,
@@ -1538,7 +1538,7 @@ func (proxier *Proxier) syncProxyRules() {
 	}
 
 	// Finish housekeeping, clear stale conntrack entries for UDP Services
-	conntrack.CleanStaleEntries(proxier.iptables.IsIPv6(), proxier.exec, proxier.svcPortMap, serviceUpdateResult, endpointUpdateResult)
+	conntrack.CleanStaleEntries(proxier.conntrack, proxier.svcPortMap, serviceUpdateResult, endpointUpdateResult)
 }
 
 func (proxier *Proxier) writeServiceToEndpointRules(natRules proxyutil.LineBuffer, svcPortNameString string, svcInfo proxy.ServicePort, svcChain utiliptables.Chain, endpoints []proxy.Endpoint, args []string) {