Unit test fix for RX TOA change

The change had an impact on unittests and we needed to adjust the test
cases a little to accomodate the change.

UNITTESTS/features/lorawan/loramac/Test_LoRaMac.cpp

@@ -77,6 +77,9 @@ TEST_F(Test_LoRaMac, initialize)
     conn.connection_u.otaa.nb_trials = 2;
     object->prepare_join(&conn, true);
 
+    channel_params_t params[] = {868300000, 0, { ((DR_5 << 4) | DR_0) }, 1};
+    LoRaPHY_stub::channel_params_ptr = params;
+
     LoRaWANTimer_stub::call_cb_immediately = true;
     EXPECT_TRUE(LORAWAN_STATUS_OK == object->initialize(NULL, my_cb));
 }

UNITTESTS/stubs/LoRaPHY_stub.cpp

@@ -416,4 +416,8 @@ uint8_t LoRaPHY::apply_DR_offset(int8_t dr, int8_t dr_offset)
     return LoRaPHY_stub::uint8_value;
 }
 
+uint32_t LoRaPHY::get_rx_time_on_air(uint8_t modem, uint16_t pkt_len)
+{
+    return LoRaPHY_stub::uint32_value;
+}