RootCanal: Misc improvements

- Remove some declared but un-implemented functions
  in DualModeController
- Move suggested_max_tx_octets and suggested_max_tx_time
  to the link layer controller
- Change the type of extended inquiry response
  to std::array<uint8_t, 240>, which accurately
  reflects the length of the response as passed
  from the HCI command

Test: m root-canal
Change-Id: I8837333f9c080454d987a9b7877d8c55e6d0c324