bpf: Check the validity of max_rdwr_access for sock local storage map iterator

The value of sock local storage map is writable in map iterator, so check
max_rdwr_access instead of max_rdonly_access.

Fixes: 5ce6e77c ("bpf: Implement bpf iterator for sock local storage map")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/r/20220810080538.1845898-6-houtao@huaweicloud.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>