Optimize tls ffi implementation, remove ffi feature cfg.

[xiaofei0800]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 70.27027% with 11 lines in your changes missing coverage. Please review.

Project coverage is 95.19%. Comparing base (64ba69d) to head (5f3b488).
Report is 188 commits behind head on develop.

Files	Patch %	Lines
src/tls/boringssl/tls.rs	64.70%	6 Missing ⚠️
src/tls/tls.rs	68.75%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #88      +/-   ##
===========================================
- Coverage    95.24%   95.19%   -0.05%     
===========================================
  Files           47       47              
  Lines        31433    31453      +20     
===========================================
+ Hits         29937    29942       +5     
- Misses        1496     1511      +15     

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