Remove errors from LocalTrafficDetector constructors

The constructors only return an error if you pass them invalid data,
but we only ever pass them data which has already been validated,
making the error checking just annoying. Just make them return garbage
output if you give them garbage input.

pkg/proxy/iptables/proxier_test.go

@@ -93,7 +93,7 @@ func NewFakeProxier(ipt utiliptables.Interface) *Proxier {
 		ipfamily = v1.IPv6Protocol
 		podCIDR = "fd00:10::/64"
 	}
-	detectLocal, _ := proxyutil.NewDetectLocalByCIDR(podCIDR)
+	detectLocal := proxyutil.NewDetectLocalByCIDR(podCIDR)
 
 	networkInterfacer := proxyutiltest.NewFakeNetwork()
 	itf := net.Interface{Index: 0, MTU: 0, Name: "lo", HardwareAddr: nil, Flags: 0}