Mitigate inconsistent test results for ROBOT (3.2)

[drwetter]

As reported a longer while back in #2083 there were trailing bytes when receiving a TLS alert by the ROBOT check.

This PR corrects and thus normalizes the length of the TLS alert message to the correct value, supposed the length in the TLS alert is two bytes and it is an TLS alert. PR for 3.3dev was #2969 .

Also this PR now introduces a separate variable for the timeout. Using a separate global variable may offer some possibility for tuning the check when the latency to the target is high. This is still subject of research. The variable is 10 seconds here to be in line with MAX_WAITSOCK which (name) was used previously.

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• Bug fix
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• Breaking change (bug fix, feature or improvement that would cause existing functionality to not work as expected)
• Typo fix
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If it's a code change please check the boxes which are applicable

• For the main program: My edits contain no tabs, indentation is five spaces and any line endings do not contain any blank chars
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• I have tested this fix or improvement against >=2 hosts and I couldn't spot a problem
• I have tested this new feature against >=2 hosts which show this feature and >=2 host which does not (in order to avoid side effects) . I couldn't spot a problem
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