Feature request: Add cisco ip sla probes support

[fcastello]

cisco ip sla feature allows to probe between devices using icmp, tcp and udp. based on https://tools.ietf.org/html/rfc6812#section-3.1.2
I would be a nice to have that cisco can probe to a cloudprober server using udp or tcp. And also cloudprober to support probes hitting a cisco device consifured with ip sla responder as a udp echo.

[xuanyuanaosheng]

@fcastello @manugarg Could you please share a configuration of the UDP Probe ?