test: lorawanstack: Use valid message type

We previously made up an invalid message type, which was roughly
`MCPS_MULTICAST | 0x40`. This causes an MBED_ASSERT failure in the
handle_rx function, as it uses an assert to validate the message type
passed to it (in convert_to_msg_flag()). Use the valid message type
MCPS_MULTICAST instead in the handle_rx unit test.

Author: Patater

connectivity/lorawan/tests/UNITTESTS/features/lorawan/lorawanstack/Test_LoRaWANStack.cpp

@@ -554,7 +554,7 @@ TEST_F(Test_LoRaWANStack, handle_rx)
     }
     ind.buffer = ind_buf;
     ind.buffer_size = 50;
-    ind.type = mcps_type_t(66);
+    ind.type = MCPS_MULTICAST;
     radio._ev->rx_done(NULL, 0, 0, 0);
     EXPECT_TRUE(50 == object->handle_rx(data, 50, port, flags, false));
     EXPECT_EQ(10, data[10]);