Fix IP address rate limit (#8758)

* Fix IP address rate limit

* CHANGELOG

* Tune getIpHash

packages/backend/src/misc/get-ip-hash.ts

@@ -0,0 +1,9 @@
+import IPCIDR from 'ip-cidr';
+
+export function getIpHash(ip: string) {
+	// because a single person may control many IPv6 addresses,
+	// only a /64 subnet prefix of any IP will be taken into account.
+	// (this means for IPv4 the entire address is used)
+	const prefix = IPCIDR.createAddress(ip).mask(64);
+	return 'ip-' + BigInt('0b' + prefix).toString(36);
+}