Clean up state when connection is failed or completed. Ignore data frome stale sockets, timers, etc.

[mickel8]

This PR:

• cleanup state after moving to the failed state
• cleanup state after moving to the completed state
• ensures we ignore all actions except ice restart when the connection is in failed state
• ensures that we ignore data from stale sockets, timers, etc. e.g. we might move to the failed state at the same time as keepalive timer fires. As a result, we will cleanup internal state at first, and then we will try to handle keepalive. The same with incoming udp data, and other timers.

[codecov]

Codecov Report

Attention: Patch coverage is 73.84615% with 17 lines in your changes missing coverage. Please review.

Project coverage is 81.79%. Comparing base (bed3d9c) to head (c4c8133).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #55      +/-   ##
==========================================
+ Coverage   80.94%   81.79%   +0.85%     
==========================================
  Files          25       25              
  Lines        1443     1483      +40     
==========================================
+ Hits         1168     1213      +45     
+ Misses        275      270       -5     

Files	Coverage Δ
lib/ex_ice/priv/conn_check_handler/controlling.ex	96.15% <100.00%> (-0.15%)	⬇️
lib/ex_ice/priv/ice_agent.ex	84.61% <72.58%> (+0.15%)	⬆️

... and 3 files with indirect coverage changes

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[LVala]

I find this syntax a bit confusing, consider using local_cand when is_struct(local_cand) <- ...