Bluetooth: Advertising resume functionality is broken

[jori-nordic]

Describe the bug

1. This feature only works when using legacy advertising
2. This feature will attempt to change the random address while a scanner/initiator is running

The Bluetooth specification says that (when using legacy advertising) it is forbidden to update the random address whilst another role is running.
That means we can't start a scanner while an advertiser is running or the opposite.

With the resume feature, it is very probable that the host attempts to re-start advertising while the scanner is already running.

Proposed change

We should deprecate that feature.
It has also been the source of many race-condition bugs (finding PRs left as exercise to the reader).

With the addition of the recycled callback, that feature is now implementable by the application itself.

zephyr/include/zephyr/bluetooth/conn.h

Lines 1003 to 1016 in e32c2ee

	/** @brief A connection object has been returned to the pool.
	*
	* This callback notifies the application that it might be able to
	* allocate a connection object. No guarantee, first come, first serve.
	*
	* Use this to e.g. re-start connectable advertising or scanning.
	*
	* Treat this callback as an ISR, as it originates from
	* @ref bt_conn_unref which is used by the BT stack. Making
	* Bluetooth API calls in this context is error-prone and strongly
	* discouraged.
	*/
	void (*recycled)(void);

Additional context

• Bluetooth: Host: Map HCI cmd disallowed to errno  #72418
• tests: Bluetooth: "fix" resume2 bsim test #72404