Al Viro discovered some breakage with the parsing of the set_ftrace_filter

as well as the removing of function probes.

This fixes the code with Al's suggestions. I also added a few selftests
to test the broken cases such that they wont happen again.
-----BEGIN PGP SIGNATURE-----
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=tVDz
-----END PGP SIGNATURE-----