doc: release-3.2: Document bt_conn_get_security and bt_conn_enc_key_size
doc: release-3.2: Document bt_conn_get_security and bt_conn_enc_key_size

Note on const modifier added to `conn` parameter.

Signed-off-by: Mariusz Skamra <c73850bd0bf85e95dce44c2ce1418ca55c1b6c5d@codecoup.pl>

galak/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr