[core,transport] reserve space in rdpTransportIo

For better ABI compatibility reserve some extra space in this public
struct.

include/freerdp/transport_io.h

@@ -33,8 +33,6 @@ extern "C"
 {
 #endif
 
-	typedef struct rdp_transport_io rdpTransportIo;
-
 	typedef int (*pTCPConnect)(rdpContext* context, rdpSettings* settings, const char* hostname,
 	                           int port, DWORD timeout);
 	typedef BOOL (*pTransportFkt)(rdpTransport* transport);
@@ -57,6 +55,7 @@ extern "C"
 		pTransportRead ReadBytes; /* Reads up to a requested amount of bytes from the transport */
 		pTransportGetPublicKey GetPublicKey;
 		pTransportSetBlockingMode SetBlockingMode;
+		UINT64 reserved[54]; /* Reserve some space for ABI compatibility */
 	};
 	typedef struct rdp_transport_io rdpTransportIo;