[rust][ethernet] Distinguish tx_echo from rx

If listen_tx is enabled for the client, it is impossible to tell whether
a Receive event is caused by tx echo or a packet that is received. So
include the flags as part of the Receive event.

Test: Verified behavior with eth-rs

Change-Id: Ice7c2353f5b634bea30ee181eb8113b345940377
6 files changed