Dual-stack clusters exist; ServiceChangeTracker does not need to log
messages (even at V(4)) when it sees dual-stack Services, and
EndpointsChangeTracker does not need to emit Events(!) when it sees
EndpointSlices of the wrong AddressType.
(Though in most cases the EndpointsChangeTracker Events would not get
emitted anyway, since the MetaProxier would ensure that only the v4
tracker saw v4 slices, and only the v6 tracker saw v6 slices.)
Also remove a nil check labeled "This should never happen" which, in
fact, we know *didn't* happen, since the function has already
dereferenced the value before it checking it against nil.
Move the ServicePort/BaseServicePortInfo types to serviceport.go.
Move the Endpoint/BaseEndpointInfo types to endpoint.go.
To avoid confusion with the new filenames, rename service.go to
servicechangetracker.go and endpoints.go to endpointschangetracker.go.
(No code changes; this just moves some code from types.go and
services.go to serviceport.go, and some code from types.go and
endpoints.go to endpoint.go.)
