Bluetooth: Add directed advertising support through connect()

When we're in peripheral mode (HCI_ADVERTISING flag is set) the most
natural mapping of connect() is to perform directed advertising to the
peer device.

This patch does the necessary changes to enable directed advertising and
keeps the hci_conn state as BT_CONNECT in a similar way as is done for
central or BR/EDR connection initiation.

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