Allow UDP port 17500 for Dropbox Lan Sync

See:
https://web.archive.org/web/20120502064502/http://geeklogs.posterous.com/dropbox-lan-sync-protocol
https://github.com/wireshark/wireshark/blob/f4b0abc7296bbb431e64e31f85b24c29196c2ae4/epan/dissectors/packet-db-lsp.c#L272

Or simply run:
   netstat -lupn | grep dropbox
while dropbox is running with LAN Sync enabled

ufw-dropbox

@@ -1,4 +1,4 @@
 [Dropbox]
 title=Dropbox LAN Sync
 description=Dropbox is a free service that lets you bring your photos, docs, and videos anywhere and share them easily
-ports=17500/tcp
+ports=17500/tcp|17500/udp