lib: set SOVERSION back to 0

When the version was incremented to 2.0.0, this resulted
in the SOVERSION being set to 2, indicating an ABI change,
which was actually not the case.

People have been complaining that software linked against
librtlsdr.so.0 is no longer working, so change the SOVERSION
back to 0.

src/CMakeLists.txt

@@ -29,7 +29,7 @@ target_include_directories(rtlsdr PUBLIC
   )
 set_target_properties(rtlsdr PROPERTIES DEFINE_SYMBOL "rtlsdr_EXPORTS")
 set_target_properties(rtlsdr PROPERTIES OUTPUT_NAME rtlsdr)
-set_target_properties(rtlsdr PROPERTIES SOVERSION ${MAJOR_VERSION})
+set_target_properties(rtlsdr PROPERTIES SOVERSION 0)
 set_target_properties(rtlsdr PROPERTIES VERSION ${LIBVER})
 generate_export_header(rtlsdr)