ICE/PJNATH: fix crashes and assertion failures

This patch introduces many changes that prevent various crashes
and assertion failures.

In PJNATH source code:
 - Avoid duplication when adding host candidates.
 - Prtoect ICE context (lock) in TCP callbacks
 - Correctly set local and remote addres in STUN request

In jami source code:
 - Check that the address is valid before using PJSIP
 helpers

Gitlab: #617

Change-Id: I317d748db8d1f93dda6d5f510a2fae909a04704c