Bluetooth: controller: Fix conn setup regression

Fix incorrect and redundant use of ticker user id ULL_LOW
instead of ULL_HIGH when setting up a connection using a
mayfly to disable LLL context. Also, the LLL context pointer
is invalid, where node rx is passed instead of LLL context.

Use the ULL disabled callback when done event has not yet
been processed, or a direct connection setup in ULL_HIGH
context when ULL is already disabled (reference count is
zero) is sufficient.

Regression introduced in commit 30f260df ("Bluetooth:
controller: Fix adv/scan context access post release").

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>