Backport of "decoder: don't reply src caps query with allowed if pad is fixed" into 1.18
requested to merge tpm/gstreamer-vaapi:backport-mr-397-into-1.18-decoder-srcpad-caps-query into 1.18
Backport of !397 (merged) "decoder: don't reply src caps query with allowed if pad is fixed".
Commits:
- 27427c00 decoder: don't reply src caps query with allowed if pad is fixed