test_kprobes: clear kprobes between test runs

test_kprobes: clear kprobes between test runs

Running the kprobes sanity tests twice makes all tests fail and
eventually crashes the kernel.

[root@martin-riscv-1 ~]# echo 1 > /sys/kernel/debug/kunit/kprobes_test/run
...
   # Totals: pass:5 fail:0 skip:0 total:5
   ok 1 kprobes_test
[root@martin-riscv-1 ~]# echo 1 > /sys/kernel/debug/kunit/kprobes_test/run
...
  # test_kprobe: EXPECTATION FAILED at lib/tests/test_kprobes.c:64
  Expected 0 == register_kprobe(&kp), but
      register_kprobe(&kp) == -22 (0xffffffffffffffea)
...
  Unable to handle kernel paging request ...

The testsuite defines several kprobes and kretprobes as static variables
that are preserved across test runs.

After register_kprobe and unregister_kprobe, a kprobe contains some
leftover data that must be cleared before the kprobe can be registered
again. The tests are setting symbol_name to define the probe location.
Address and flags must be cleared.

The existing code clears some of the probes between subsequent tests, but
not between two test runs. The leftover data from a previous test run
makes the registrations fail in the next run.

Move the cleanups for all kprobes into kprobes_test_init, this function
is called before each single test (including the first test of a test
run).

Link: https://lore.kernel.org/all/20260507134615.1010905-1-martin@kaiser.cx/
Fixes: e44e81c5b90f ("kprobes: convert tests to kunit")
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>