Extract mtproto key generation code.

Telegram/SourceFiles/mtproto/connection_abstract.cpp

@@ -12,6 +12,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "mtproto/connection_resolving.h"
 #include "mtproto/session.h"
 #include "base/unixtime.h"
+#include "base/openssl_help.h"
 
 namespace MTP {
 namespace internal {
@@ -187,5 +188,11 @@ ConnectionPointer AbstractConnection::Create(
 	return result;
 }
 
+uint32 AbstractConnection::extendedNotSecurePadding() const {
+	return requiresExtendedPadding()
+		? uint32(openssl::RandomValue<uchar>() & 0x3F)
+		: 0;
+}
+
 } // namespace internal
 } // namespace MTP