Show difference in called functions

[viktormalik]

It often happens that a function is both renamed and re-implemented at the same time. When comparing its caller function, we only show the difference caused by the renaming.

It would be nice if we were able to detect such a situation and show the difference from the function itself, which is more important.

This occurs, e.g., when comparing function __put_task_struct between kernels 4.18.0-147.el8 and 4.18.0-193.el8.