* the Ethernet frame specified in 'packet' taken from the flow specified in
* the 'key_len' bytes of 'key'. ('key' is mostly redundant with 'packet', but
* it contains some metadata that cannot be recovered from 'packet', such as
* the Ethernet frame specified in 'packet' taken from the flow specified in
* the 'key_len' bytes of 'key'. ('key' is mostly redundant with 'packet', but
* it contains some metadata that cannot be recovered from 'packet', such as