fix issues in vaapi buffer pool set_config()
commit 46f9c901
vaapivideobufferpool: reject configuration if allocator isn't vaapi
If the requested allocator in set_config() is not a VAAPI valid one,
reject the configuration, instead of lying and using a private one.
This patch superseeds !254 and !24
commit 2cca51ca
vaapivideobufferpool: add explanation for allocator reconfig
commit f6430342
vaapivideobufferpool: check for vaapi meta first
If the configured meta doesn't request vaapi meta then it is not a
vaapi buffer pool. Bail out as soon as possible.
commit 8f5aad51
vaapivideobufferpool: turn errors into warnings
set_config() vmethod should fail gracefully, thus upstream could
negotiate another pool if possible.
Instead of sending error messages to the bus, let demote the level
to warning.