rusty-gd: hci facade completes command to ACK receive

do this before sending, to ensure we don't block waiting
for events that will never come (in the case of loopback)

Bug: 171749953
Tag: #gd-refactor
Test: gd/cert/run --rhost
Change-Id: I71b8d3f5737769d844ca5d44bbeebd069aed52b3