Convert for util.IP to just use a net.IP

pflag can handle IP addresses so use the pflag code instead of doing it
ourselves. This means our code just uses net.IP and we don't have all of
the useless casting back and forth!

pkg/util/net.go

@@ -17,30 +17,10 @@ limitations under the License.
 package util
 
 import (
-	"fmt"
 	"net"
 	"strings"
 )
 
-// IP adapts net.IP for use as a flag.
-type IP net.IP
-
-func (ip IP) String() string {
-	return net.IP(ip).String()
-}
-
-func (ip *IP) Set(value string) error {
-	*ip = IP(net.ParseIP(strings.TrimSpace(value)))
-	if *ip == nil {
-		return fmt.Errorf("invalid IP address: '%s'", value)
-	}
-	return nil
-}
-
-func (*IP) Type() string {
-	return "ip"
-}
-
 // IPNet adapts net.IPNet for use as a flag.
 type IPNet net.IPNet