Remove duplicate code

client/firewall/uspfilter/filter.go

@@ -56,12 +56,6 @@ const (
 
 var errNatNotSupported = errors.New("nat not supported with userspace firewall")
 
-// serviceKey represents a protocol/port combination for netstack service registry
-type serviceKey struct {
-	protocol gopacket.LayerType
-	port     uint16
-}
-
 // RuleSet is a set of rules grouped by a string key
 type RuleSet map[string]PeerRule