Bluetooth: Set LE advertising parameters before enabling it

The LE advertising parameters can only be modified when advertising
is disabled. So before enabling it, make sure the controller has all
the right parameters.

Right now all default values are used and thus this does no change
any existing behavior. One minor exception is that in case of single
mode LE-only controllers without a public address, now the random
address is used for advertising.

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