Fix version and soversion of libKF5Torrent.so.
This changes version of so file
Before: libKF5Torrent.so->libKF5Torrent.so.6->libKF5Torrent.so.6.0.0
After: libKF5Torrent.so->libKF5Torrent.so.6->libKF5Torrent.so.20.11.17
I.e. soversion is kept at 6 until we have ABI changes but version is set to actual version instead of arbitrary 6.0.0.