Remove the $mac variable from vif-route-qubes

It was used to add appropriate neighbor entries, but Qubes OS no longer
does that.  Hard-code a reasonable value in vif-qubes-nat.

network/vif-qubes-nat.sh

@@ -26,7 +26,7 @@ netns_appvm_if="${vif}"
 #               '----------------------------------'
 #
 
-readonly netvm_mac=fe:ff:ff:ff:ff:ff
+readonly netvm_mac=fe:ff:ff:ff:ff:ff mac=00:16:3e:5e:6c:00
 
 function run
 {

network/vif-route-qubes

@@ -121,8 +121,6 @@ case "$command" in
         iptables_cmd='-I PREROUTING 1'
         cmdprefix=''
         ipv6_disabled=$(cat "/proc/sys/net/ipv6/conf/$vif/disable_ipv6" || echo 1)
-        # without a MAC address we will fail later with a confusing error
-        mac=$(xenstore-read "backend/vif/$domid/$sub/mac") || exit 1
         ;;
     offline)
         do_without_error ifdown "${vif}"