Make ownership of avs_net_psk_t pointers explicit
Make ownership of avs_net_psk_t pointers explicit

Summary:
- Add avs_net_owned_psk_t, add const to avs_net_psk_t
- Add comments to avs_net_psk_t and avs_net_owned_psk_t

Test Plan: make check

Reviewers: kfyatek!, mkrawiec!

Differential Revision: https://phabricator.avsystem.com/D5018

AVSystem/avs_commons,AVSystem/avs_commons,AVSystem/avs_commons,AVSystem/avs_commons