bpf_rbtree_left
BTF_ID_FLAGS(func, bpf_rbtree_left, KF_RET_NULL)
BTF_ID(func, bpf_rbtree_left)
rb_n = bpf_rbtree_left(&groot0, rb_n);
rb_n = bpf_rbtree_left(&root, rb_n);
rb_n = bpf_rbtree_left(&root_r, rb_n);