Bluetooth: Rename hci_send_to_control to hci_send_to_channel

The hci_send_to_control() can be made more general purpose with a small
change of passing the desired HCI channel as a parameter to it. This
allows using it for the monitor channel as well as e.g. 6lowpan in the
future.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>