lncfg: use net pkg IsLoopback method

Use the IsLoopback method provided by the net package instead of using
hardcoded loopback addresses.

lncfg/address.go

@@ -14,10 +14,6 @@ import (
 	"github.com/lightningnetwork/lnd/tor"
 )
 
-var (
-	loopBackAddrs = []string{"localhost", "127.0.0.1", "[::1]"}
-)
-
 // TCPResolver is a function signature that resolves an address on a given
 // network.
 type TCPResolver = func(network, addr string) (*net.TCPAddr, error)
@@ -112,14 +108,18 @@ func TLSListenOnAddress(addr net.Addr,
 }
 
 // IsLoopback returns true if an address describes a loopback interface.
-func IsLoopback(addr string) bool {
-	for _, loopback := range loopBackAddrs {
-		if strings.Contains(addr, loopback) {
-			return true
-		}
+func IsLoopback(host string) bool {
+	if strings.Contains(host, "localhost") {
+		return true
 	}
 
-	return false
+	rawHost, _, _ := net.SplitHostPort(host)
+	addr := net.ParseIP(rawHost)
+	if addr == nil {
+		return false
+	}
+
+	return addr.IsLoopback()
 }
 
 // isIPv6Host returns true if the host is IPV6 and false otherwise.