Bluetooth: Fix advertising and active scanning co-existence

Many controllers allow simultaneous active scanning and advertising
(e.g. Intel and Broadcom) but some do not (e.g. CSR). It's therefore
safest to implement mutual exclusion of these states in the kernel.

This patch ensures that the two states are never entered simultaneously.
Extra precaution needs to be taken for outgoing connection attempts in
slave role (i.e. through directed advertising) in which case the
operation that came first has precedence and the one that comes after
gets a rejection.

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