wallet: use mutex protected random generation api

src/simplewallet/simplewallet.cpp

@@ -1784,7 +1784,7 @@ bool simple_wallet::print_integrated_address(const std::vector<std::string> &arg
   }
   if (args.size() == 0)
   {
-    crypto::generate_random_bytes(8, payment_id.data);
+    payment_id = crypto::rand<crypto::hash8>();
     success_msg_writer() << tr("Random payment ID: ") << payment_id;
     success_msg_writer() << tr("Matching integrated address: ") << m_wallet->get_account().get_public_integrated_address_str(payment_id, m_wallet->testnet());
     return true;

src/wallet/wallet_rpc_server.cpp

@@ -356,7 +356,7 @@ namespace tools
       crypto::hash8 payment_id;
       if (req.payment_id.empty())
       {
-        crypto::generate_random_bytes(8, payment_id.data);
+        payment_id = crypto::rand<crypto::hash8>();
       }
       else
       {