TT#125900 Do not validate IP on OpenVPN interface 'tun'

NGCP has two VPN connections (types in network.yml):
 - openvpn
 - openvpn_vip
The second one should have identical IP on sp1 and sp2,
therefor we have to disable validation for 'tun' interface
(like we have for 'dummy' already).

Change-Id: Ia49d22d4c448a2d77db6a6cd7e755ec2f19a8d7b

sbin/ngcp-network-validator

@@ -162,7 +162,7 @@ foreach my $hostname (sort keys %{$yaml->{hosts}}) {
         if (defined $host->{$iface}->{ip} and
             $host->{$iface}->{ip} ne '' and
             $host->{$iface}->{ip} ne '127.0.0.1' and
-            $iface !~ m/^dummy/) {
+            $iface !~ m/^dummy/ and $iface !~ m/^tun/) {
             push @{$dupe_ip{$host->{$iface}->{ip}}}, "$hostname/$iface";
         }
         if ($hwaddr_dupe_check and