update qemu -device virtio-net-device in examples/riscv/Makefile. Now we can see virtio NIC device info in this example

examples/riscv/Makefile

@@ -62,10 +62,9 @@ qemu: kernel $(img)
 		-device virtio-blk-device,drive=x0 \
 		-device virtio-gpu-device \
 		-device virtio-mouse-device \
-		# -netdev type=tap,id=net0,script=no,downscript=no \
-		# -device virtio-net-device,netdev=net0
+		-device virtio-net-device
 
 $(img):
 	dd if=/dev/zero of=$@ bs=512 count=32
 
-run: build qemu-legacy qemu
+run: build qemu-legacy qemu