/usr/lib/mysql/plugin/libfnv_udf.so.0 is in percona-xtradb-cluster-server-5.5 5.5.34-25.9+dfsg-0ubuntu4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/mysql/plugin/libfnv_udf.so.0.0.0
/usr/lib/mysql/plugin/libfnv_udf.so.0.0.0