TLS 1.2 on signaling tcp.

Signal/src/network/tcp/tls/SecureEndPoint.m

@@ -38,10 +38,10 @@
 }
 
 -(void) handleStreamsOpened:(StreamPair *)streamPair {
-    [[streamPair inputStream] setProperty:NSStreamSocketSecurityLevelNegotiatedSSL
+    [[streamPair inputStream] setProperty:(__bridge id)CFSTR("kNSStreamSocketSecurityLevelTLSv1_2")
                                    forKey:NSStreamSocketSecurityLevelKey];
     
-    [[streamPair outputStream] setProperty:NSStreamSocketSecurityLevelNegotiatedSSL
+    [[streamPair outputStream] setProperty:(__bridge id)CFSTR("kNSStreamSocketSecurityLevelTLSv1_2")
                                     forKey:NSStreamSocketSecurityLevelKey];
     
     NSDictionary *settings = @{(id)kCFStreamSSLValidatesCertificateChain: @NO,