selftests/livepatch: add test for module function patching

selftests/livepatch: add test for module function patching

Add a target module and livepatch pair that verify module function
patching via a proc entry. Two test cases cover both the
klp_enable_patch path (target loaded before livepatch) and the
klp_module_coming path (livepatch loaded before target).

Signed-off-by: Pablo Alessandro Santos Hugen <phugen@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Link: https://patch.msgid.link/20260320201135.1203992-1-phugen@redhat.com
Signed-off-by: Petr Mladek <pmladek@suse.com>