selftests/bpf: Make bpf_dynptr_is_rdonly() prototyype consistent with kernel

Currently kernel kfunc bpf_dynptr_is_rdonly() has prototype ...

  __bpf_kfunc bool bpf_dynptr_is_rdonly(struct bpf_dynptr_kern *ptr)

... while selftests bpf_kfuncs.h has:

  extern int bpf_dynptr_is_rdonly(const struct bpf_dynptr *ptr) __ksym;

Such a mismatch might cause problems although currently it is okay in
selftests. Fix it to prevent future potential surprise.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230517040409.4024618-1-yhs@fb.com

tools/testing/selftests/bpf/bpf_kfuncs.h

@@ -37,7 +37,7 @@ extern void *bpf_dynptr_slice_rdwr(const struct bpf_dynptr *ptr, __u32 offset,
 
 extern int bpf_dynptr_adjust(const struct bpf_dynptr *ptr, __u32 start, __u32 end) __ksym;
 extern bool bpf_dynptr_is_null(const struct bpf_dynptr *ptr) __ksym;
-extern int bpf_dynptr_is_rdonly(const struct bpf_dynptr *ptr) __ksym;
+extern bool bpf_dynptr_is_rdonly(const struct bpf_dynptr *ptr) __ksym;
 extern __u32 bpf_dynptr_size(const struct bpf_dynptr *ptr) __ksym;
 extern int bpf_dynptr_clone(const struct bpf_dynptr *ptr, struct bpf_dynptr *clone__init) __ksym;