fix TestPeerConnection_Simulcast_RTX on v3

[aalekseevx]

Newly added test could not pass as simulcast extension headers are not enabled by default on v3

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 78.54%. Comparing base (eb6e395) to head (e029893).
Report is 9 commits behind head on v3.

Files	Patch %	Lines
interceptor.go	33.33%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##               v3    #2769      +/-   ##
==========================================
+ Coverage   76.32%   78.54%   +2.21%     
==========================================
  Files          87       87              
  Lines        9846     8127    -1719     
==========================================
- Hits         7515     6383    -1132     
+ Misses       1866     1276     -590     
- Partials      465      468       +3     

Flag	Coverage Δ
go	80.13% <33.33%> (+2.27%)	⬆️
wasm	65.09% <ø> (+0.64%)	⬆️

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[Sean-Der]

Thank you @aalekseevx !