fix bug in vlan filtered netmap, duplicate nodes

lib/App/Netdisco/Web/Plugin/Device/Neighbors.pm

@@ -216,7 +216,10 @@ ajax '/ajax/data/device/netmap' => require_login sub {
       );
     }
 
+    my %seen_node = ();
     DEVICE: while (my $device = $devices->next) {
+      next if $seen_node{$device->ip};
+
       # if in neighbors mode then use %ok_dev to filter
       next DEVICE if ($device->ip ne $qdev->ip)
         and ($mapshow eq 'neighbors')
@@ -269,6 +272,8 @@ ajax '/ajax/data/device/netmap' => require_login sub {
       }
 
       push @{$data{'nodes'}}, $node;
+      ++$seen_node{$device->ip};
+
       $metadata{'centernode'} = $device->ip
         if $qdev and $qdev->in_storage and $device->ip eq $qdev->ip;
     }