Reworked update code, split v4/v6 updates

- collect dns updatees individually, so that we clear A and AAAA separately if and only if needed.
- made nft AddIP call more resilient against partial updates
- updated nft processing code to no longer add nil to a v4/v6 set which would end in an invalid call to AddIP when updating nft. call it individually now.
- updated samples with real world traces from an AVM Box

service/nftables.go

@@ -65,6 +65,9 @@ func (nut *NFTUpdateTable) FindOrAddSet(SetName string, IP6 bool) (*NFTUpdateSet
 }
 
 func (nu *NFTUpdate) AddIP(TableName string, SetName string, IP net.IP) error {
+	if IP == nil {
+		return nil
+	}
 	ip6 := (IP.To4() == nil)
 	nut := nu.FindOrAddTable(TableName)
 	nus, err := nut.FindOrAddSet(SetName, ip6)