RootCanal: Implement HCI parameter validation for LE connection commands

- Implement HCI parameter validation for LE Create Connection and
  LE Extended Create Connection commands
- Group the initiator state parameters into a sub-class
  LinkLayerController::Initiator

The LE Connection logic in ConnectIncomingLegacyAdvertisingPdu and
ConnectIncomingExtendedAdvertisingPdu is unchanged

Test: atest rootcanal_hci_test
Change-Id: I5db4372effbb373aa994a6dca91e212e373fd151