sflow - Error handing counter record type - Invalid counter record type: 2001

Hello,

I am generating sample sflow data using [host-sflow](https://github.com/sflow/host-sflow) daemon for testing purposes. Gopacket is failing to decode certain packets. e.g. [counter record type 2001](https://github.com/sflow/host-sflow/blob/dc692defd23473a16a388d9123cc4a292889ccef/src/sflow/sflow.h#L1227). I see that gopacket supports only [limited](https://github.com/google/gopacket/blob/3aa782ce48d4a525acaebab344cedabfb561f870/layers/sflow.go#L735) number of counter packet types.

Would like to know why other counter packet types are not handled today.

Thanks,
Siddharth