tests.jumbo:Fix get_linux_ifname() error

get_linux_ifname() has been moved from utils_test into utils_net.
But the commit 7db6cc4db5ba5d86659839b4afee96603c346520
change it back to utils_test for linux.

Signed-off-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>