Assign STUN and TURN as default candidate only when the resolution/allocation is complete (thanks Stephen D. Strowes for the suggestion)

[bennylp]

Quoting Stephen's email:

At the moment, the default seems to be set while possibly still pending
full initialisation (e.g., if I set stun-srv, the default_cand is set to
indicate that this is the default candidate while STUN is still pending
a response; if a response never arrives, then the default candidate addr
is 0.0.0.0, and things may then fall over on attempting a call).


Would it make more sense to only set the default candidate to the HOST
address on init, and then subsequently set the default candidate inside
the stun_on_status() and turn_on_status() functions, if a more
appropriate default becomes available?

[nanang]

TeluuCon2019: a valid issue, solution: only update the default candidate to STUN candidate when STUN binding has been completed successfully (like in TURN).