doc: releases: add Bluetooth privacy changes for extended advertising

Added new entries in the release notes for the upcoming v3.2 Zephyr
release that describe recent Bluetooth Privacy changes for the
Extended Advertising from the following PR:

https://github.com/zephyrproject-rtos/zephyr/pull/47260



Signed-off-by: Kamil Piszczek <Kamil.Piszczek@nordicsemi.no>