Implement IP depacketizer

[rowanG077]

Feature description
This is a depacketizer similar to MAC packetizer #25

Expected behaviour
The bytes containing the IP header are stripped of the packet stream and parsed into the metaType.

Expected steps
This can be achieved using the generic dpacketizer from #25. The expected type is:

fromIPFrame
  :: HiddenClockResetEnable dom
  => Circuit (PacketStream dom n EthernetHeader) (PacketStream dom n IPHeader)

Perhaps it's better to first define a IPHeaderLite which only contains the fields which we support and then a seperate IPHeader -> IPHeaderLite function sets all fields to constants.

This plays nicely with the mapping functions in the generic depacketizer.

Additional context
Note here is that the header has a checksum. This needs to be validated. So it depends on #75.