Fix corruption of certain packets containing invalid TLS extension fields

[arjunbhat1]

Fixes #3853

Scapy's TLS layer corrupts packet data in some cases during dissection of TLS records containing invalid extension fields (extlen != len(ext)).

A corresponding unit test has been added as well.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.62%. Comparing base (c38a5de) to head (6cc0246).
Report is 6 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4554   +/-   ##
=======================================
  Coverage   81.61%   81.62%           
=======================================
  Files         356      356           
  Lines       85540    85542    +2     
=======================================
+ Hits        69816    69824    +8     
+ Misses      15724    15718    -6     

Files with missing lines	Coverage Δ
scapy/layers/tls/extensions.py	83.90% <100.00%> (+0.10%)	⬆️

... and 7 files with indirect coverage changes

[gpotter2]

Thanks for the PR !