capi: Expose RDO lookahead frames
capi: Expose RDO lookahead frames

This was missed in 2db1f9c81f033fcd1eb421236b52036ee74b03f2.

API ADDITION.

Signed-off-by: Derek Buitenhuis <aff7d637ede26ea82e5226e01b697996cc52e526@gmail.com>

xiph/rav1e,xiph/rav1e