Bluetooth: Disallow LE scanning and connecting in peripheral role

When an adapter is in the LE peripheral role scanning for other devices
or initiating connections to them is not allowed. This patch makes sure
that such attempts will result in appropriate error returns.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>