CLEANUP: rename possibly confusing struct field "tracked"

CLEANUP: rename possibly confusing struct field "tracked"

When reading the code, the "tracked" member of a server makes one
think the server is tracked while it's the opposite, it's a pointer
to the server being tracked. This is particularly true in constructs
such as :

	if (srv->tracked) {

Since it's the second time I get caught misunderstanding it, let's
rename it to "track" to avoid the confusion.