Toggle off IC.EnableExternalDataChannel by default (#25861)

Author: mregrock

ydb/core/protos/config.proto

@@ -490,7 +490,7 @@ message TInterconnectConfig {
     optional bool SuppressConnectivityCheck = 39 [default = false];
     optional uint32 PreallocatedBufferSize = 40;
     optional uint32 NumPreallocatedBuffers = 41;
-    optional bool EnableExternalDataChannel = 42 [default = true];
+    optional bool EnableExternalDataChannel = 42 [default = false];
     optional bool ValidateIncomingPeerViaDirectLookup = 44;
     optional uint32 SocketBacklogSize = 45; // SOMAXCONN if not set or zero
     optional ESocketSendOptimization SocketSendOptimization = 51 [default = IC_SO_DISABLED];