selftests/bpf: Add selftest for calling global functions from freplace

commit 2cf7b7ff upstream.

Add a selftest that calls a global function with a context object parameter
from an freplace function to check that the program context type is
correctly converted to the freplace target when fetching the context type
from the kernel BTF.

v2:
- Trim includes
- Get rid of global function
- Use __noinline

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/20220606075253.28422-2-toke@redhat.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>
[ backport: fix conflict because tests were not serialised ]
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>