clarify apiserver bind-address flag usage

From the listen godoc:

For TCP networks, if the host in the address parameter is empty or a
literal unspecified IP address, Listen listens on all available unicast
and anycast IP addresses of the local system.

Since the BindNetwork options is "tcp" by default, using an unspecified
address doesn't bind the listener to the IP family.

Author: aojea

staging/src/k8s.io/apiserver/pkg/server/options/serving.go

@@ -143,7 +143,7 @@ func (s *SecureServingOptions) AddFlags(fs *pflag.FlagSet) {
 	fs.IPVar(&s.BindAddress, "bind-address", s.BindAddress, ""+
 		"The IP address on which to listen for the --secure-port port. The "+
 		"associated interface(s) must be reachable by the rest of the cluster, and by CLI/web "+
-		"clients. If blank, all interfaces will be used (0.0.0.0 for all IPv4 interfaces and :: for all IPv6 interfaces).")
+		"clients. If blank or an unspecified address (0.0.0.0 or ::), all interfaces will be used.")
 
 	desc := "The port on which to serve HTTPS with authentication and authorization."
 	if s.Required {