network: do not assume IPv6 gateway is a link-local address

If IPv6 gateway address provided by dom0 isn't a link local address, add
a /128 route to it. Also, add this address on backend interfaces (vif*).

This is to allow proper ICMP host unreachable packets forwarding - if
gateway (address on vif* interface) have only fe80: address, it will be
used as a source for ICMP reply. It will be properly delivered to the VM
directly connected there (for example from sys-net to sys-firewall), but
because of being link-local address, it will not be forwarded any
further.
This results timeouts if host doesn't have IPv6 connectivity.

network/setup-ip

@@ -91,6 +91,9 @@ __EOF__
         fi
         /sbin/ifconfig "$INTERFACE" up
         /sbin/route add -host "$gateway" dev "$INTERFACE"
+        if [ -n "$gateway6" ] && ! echo "$gateway6" | grep -q "^fe80:"; then
+            /sbin/route -6 add "$gateway6/128" dev "$INTERFACE"
+        fi
         if ! qsvc disable-default-route ; then
             /sbin/route add default gw "$gateway"
             if [ -n "$gateway6" ]; then

network/vif-route-qubes

@@ -40,10 +40,12 @@ if [ "${ip}" ]; then
     # IPs as seen by this VM
     netvm_ip="$ip4"
     netvm_gw_ip=$(qubesdb-read /qubes-netvm-gateway)
+    netvm_gw_ip6=$(qubesdb-read /qubes-netvm-gateway6 || :)
     netvm_dns1_ip=$(qubesdb-read /qubes-netvm-primary-dns)
     netvm_dns2_ip=$(qubesdb-read /qubes-netvm-secondary-dns)
 
     back_ip="$netvm_gw_ip"
+    back_ip6="$netvm_gw_ip6"
 
     # IPs as seen by the VM - if other than $netvm_ip
     appvm_gw_ip="$(qubesdb-read "/mapped-ip/$ip4/visible-gateway" 2>/dev/null || :)"
@@ -107,6 +109,9 @@ if [ "${ip}" ] ; then
             ${cmdprefix} flock $lockfile ip6tables-restore --noflush
     fi
     ${cmdprefix} ip addr "${ipcmd}" "${back_ip}/32" dev "${vif}"
+    if [ "${back_ip6}" ] && [[ "${back_ip6}" != "fe80:"* ]]; then
+        ${cmdprefix} ip addr "${ipcmd}" "${back_ip6}/128" dev "${vif}"
+    fi
 fi
 
 log debug "Successful vif-route-qubes $command for $vif."