Function get_proxy_safety

pub fn get_proxy_safety(option: u16) -> ProxySafety

Extract the option’s proxy safety bit(s)

assert_eq!(get_proxy_safety(ETAG), ProxySafety::SafeToForward { cache_key: true });
assert_eq!(get_proxy_safety(SIZE1), ProxySafety::SafeToForward { cache_key: false });
assert_eq!(get_proxy_safety(BLOCK1), ProxySafety::Unsafe);