Bluetooth: Controller: Fix corrupt AD data after directed advertising

Fix corrupt AD data used after directed advertising by
storing a backup of the AD data before switching to directed
advertising. Restore back the AD data with switching to non-
directed advertising.

The fix also addresses AD data backup when switching between
Legacy and Extended Advertising.

Fixes #18850.

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