Bluetooth: Move handling of HCI_RUNNING flag into core

Setting and clearing of HCI_RUNNING flag in each and every driver is
just duplicating the same code all over the place. So instead of having
the driver do it in their hdev->open and hdev->close callbacks, set it
globally in the core transport handling.

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