selftests/bpf: Add test_verifier support to fixup kfunc call insns

selftests/bpf: Add test_verifier support to fixup kfunc call insns

BugLink: https://bugs.launchpad.net/bugs/1986728
commit 0201b80772ac2b712bbbfe783cdb731fdfb4247e upstream.

This allows us to add tests (esp. negative tests) where we only want to
ensure the program doesn't pass through the verifier, and also verify
the error. The next commit will add the tests making use of this.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220114163953.1455836-9-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
[PHLin: backport due to lack of fixup_map_timer]
Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>