[IP] Silence "TCP operation failed" debug spam

as reported for example in CORE-14097.
This log-spamming is so annoying, that ThFabba silenced it in 0.4.8-dev-1078-gad68422.
It is very widespread and affects almost every networking application, e.g. rapps, Opera, and so on...

I do prefer to have a ticket for merging the fix back.