use new qemu options for network devices

this omits warnings about deprecated options

dev-utils/fai-kvm

@@ -2,7 +2,7 @@
 
 # fai-kvm, start kvm host for testing FAI software
 #
-# Author:    Thomas Lange, Uni Koeln, 2011-2020
+# Author:    Thomas Lange, Uni Koeln, 2011-2021
 # License:   GPL v2 or any later version
 
 fix="-k en-us -smp 2 -cpu host -global isa-fdc.driveA= "  # if loading cirrusfb (via pcimodules and modprobe cirrusfb) causes errors in kvm
@@ -118,7 +118,7 @@ fi
 if ! [[ $user =~ ^[0-9]+$ ]] ; then
     die 2 "Error: Option -u needs a number"
 fi
-hex=$(printf %X $user)
+hex=$(printf %02X $user)
 diskfile=$diskdir/faitest-disk-$user
 
 if [ $daemonize -eq 1 ]; then
@@ -135,9 +135,10 @@ fi
 mac=$macprefix:$hex
 
 if [ $usernet = 1 ]; then
-    net="-net nic,name=eth0,model=virtio -net user,name=eth0"
+    net="-device virtio-net-pci,netdev=net0 -netdev user,id=net0"
 else
-    net="-net nic,macaddr=$mac,model=virtio -net tap,ifname=tap$user,script=no,downscript=no"
+    net="-device virtio-net-pci,netdev=net0,mac=$mac -netdev tap,ifname=tap$user,id=net0,script=no,downscript=no
+"
 fi