Bluetooth API called before finished initialization.

[joerchan]

Describe the bug
Some Bluetooth API function does not check for if the bluetooth device has finished initialized. This can lead to undefined behavior as the stack is operating on uninitialized kernel objects and memory.

To Reproduce
Steps to reproduce the behavior:
Call public API functions before calling bt_enable, or directly after bt_enable when supplied a ready callback.
Affected APIs:
OOB API
Gatt Notification and Indication
HCI commands

Expected behavior
APIs should return error code consistent with the rest of the API.

Impact
Undefined behavior. Minor annoyance, application should be able to not end up in this situation.

[joerchan]

Accidental enter hit. Will update description.