fix: align maxUselessRecords with OpenSSL/BoringSSL (16 → 32) to mitigate TLS stack fingerprinting

[6Kmfi6HP]

Problem

The current maxUselessRecords value is set to 16, directly copied from Go's crypto/tls standard library. However, the mainstream TLS stacks used by most web servers have a different threshold:

TLS Stack	ChangeCipherSpec / Empty AppData threshold
BoringSSL (Chrome, Cloudflare)	32
OpenSSL	32
Apple Security Framework (Safari)	32
Go crypto/tls	16
XTLS REALITY (current)	16

This discrepancy creates a detectable behavioral fingerprint. An active prober can:

1. Replay a captured VLESS REALITY Client Hello, inject ChangeCipherSpec records, and observe the server error at record Add post-handshake records detection #17 (Go behavior).
2. Send a tampered Client Hello to trigger the fallback mechanism, inject CCS records, and observe the fallback destination error at record #33 (OpenSSL/BoringSSL behavior).
3. The mismatch between 16 and 32 across two probes on the same port definitively reveals that two different TLS stacks coexist — a strong indicator of REALITY's fallback architecture.

Fix

Change maxUselessRecords from 16 to 32 to align with the behavior of BoringSSL, OpenSSL, Safari, and Cloudflare.

-	maxUselessRecords          = 16           // maximum number of consecutive non-advancing records
+	maxUselessRecords          = 32           // maximum number of consecutive non-advancing records

Rationale for value 32

• BoringSSL: shared counter of 32 for CCS + empty AppData (source)
• OpenSSL 1.1.1+: Same threshold of 32 for the shared non-advancing record counter

Note on prior art

This same discrepancy was already identified and fixed on the client side in uTLS via refraction-networking/utls#171, but the corresponding server-side code in XTLS/REALITY was never updated.

Scope

This is a necessary but not sufficient fix:

• Eliminates the CCS counter discrepancy for this specific fingerprinting vector
• Other behavioral differences between TLS stacks may still exist and should be addressed separately

Impact

• Security: Eliminates one known fingerprinting vector used in active probing
• Compatibility: No impact on normal TLS operation; 32 is still a conservative DoS protection threshold
• Performance: Negligible

[6c67b9]

#27 duplicated