Release IP address on session stop

[Zensey]

Symptoms:

invalid config to consumer request with nil instead of ip address.
like this:
{"local_port":0,"remote_port":0,"ports":null,"provider":{"public_key":"iixI/brFnGk5JPADWVhzum2WltsMV2A8iabJKgJuWQo=","endpoint":"46.14.127.237:57757"},"consumer":{"ip_address":"\u003cnil\u003e","dns_ips":"\u003cnil\u003e"}}

Cause:
IP is allocated for consumer on session start, but never gets released. Given the limited size of IP pool, exhaustion can happen in a few days or hours.

[soffokl]

The same are done in the next line, no?

[Zensey]

Fixed

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 37.97%. Comparing base (4a517cd) to head (483c458).
Report is 66 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5970      +/-   ##
==========================================
+ Coverage   37.90%   37.97%   +0.06%     
==========================================
  Files         371      371              
  Lines       20665    20715      +50     
==========================================
+ Hits         7833     7866      +33     
- Misses      12054    12064      +10     
- Partials      778      785       +7     

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