/usr/lib/x86_64-linux-gnu/librtfilter.so is in librtfilter-dev 1.1-4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/librtfilter.so.1.0.1
/usr/lib/x86_64-linux-gnu/librtfilter.so.1.0.1