Fix bundle-only data channel startup

[zshang-oai]

Pion currently treats every zero-port application m= section as rejected. This violates RFC 8843, Section 6, which permits a bundled m= section to use port zero with a=bundle-only.

Start SCTP when the application section has either a nonzero port or a=bundle-only. Zero-port sections without a=bundle-only remain rejected.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.48%. Comparing base (6a5d2f8) to head (79bf622).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3447      +/-   ##
==========================================
- Coverage   85.54%   85.48%   -0.06%     
==========================================
  Files          81       81              
  Lines        9856     9857       +1     
==========================================
- Hits         8431     8426       -5     
- Misses       1005     1011       +6     
  Partials      420      420              

Flag	Coverage Δ
go	85.48% <100.00%> (-0.06%)	⬇️

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[JoTurk]

Thank you so much.