RootCanal: Simplify HciTransport interface

HciTransport typically do not need to handle
HCI packets by type; the current interface makes it
verbose to implement a new HciTransport.

- Merge SendEvent, SendAcl, SendSco, SendIso into
  a unique Send method
- Merge CommandCallback, AclCallback, ScoCallback, IsoCallback
  into a unique PacketCallback handler

Bug: 279665786
Test: m root-canal
Change-Id: I55d1d7a35eb4d321af98e8c97d5a47f9d3f70d24