selftests/bpf: add freplace of BTF-unreliable main prog test

Add a test validating that freplace'ing another main (entry) BPF program
fails if the target BPF program doesn't have valid/expected func proto BTF.

We extend fexit_bpf2bpf test to allow to specify expected log message
for negative test cases (where freplace program is expected to fail to
load).

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231215011334.2307144-11-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>