only issue ulTickleMe for libURL sockets

The ulTickleMe messages is currently issued once a second if there are any open sockets. This is overbroad, in that if I "accept connections on socket x" and then issue an http request (for example to query whether there are any updates) then the ulTickleMe message will continue in perpetuity rather than ending when the http request finishes. This patch checks for only libUrl sockets instead of for sockets in general. The ulTickleMe messages properly stop when the libUrl command ends.