websocketimpl: avoid string copy unless logging trace message

[xkommando]

Description

avoid string copy in web socket frame decoding

Related Issue

Motivation and Context

before decoding frames, the implementation logs the first 1000 char from the socket buffer. a string object is created even if log is disabled.
changes: check the logging level before creating the logging parameters

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
  [x] minor improvement

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.