Bluetooth: Make Fast Connectable available while powered off

To maximize the usability of the Fast Connectable feature we should make
it possible to set (or unset) it at any given moment. This means
removing the dependency on the 'connectable' setting as well as the
'powered' setting. The former makes also sense since page scan may get
enabled through add_device even if 'connectable' is false. To keep the
setting available over power cycles its flag also needs to be removed
from the flags that are cleared upon HCI_Reset.

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