Fixed set channel unit test

Author: Jarkko Paso

test/nanostack/unittest/mac/fhss_callbacks/test_fhss_callbacks.c

@@ -123,6 +123,7 @@ bool test_mac_set_channel()
     arm_device_driver_list_s dev_driver;
     phy_driver.phy_tx_done_cb = tx_done;
     dev_driver.phy_driver = &phy_driver;
+    memset(&setup, 0, sizeof(protocol_interface_rf_mac_setup_s));
     setup.fhss_api = &fhss_api;
     setup.dev_driver = &dev_driver;
     mac_mlme_stub.int8_value = 0;