bus-util: change Default-chopping to Limit-searching

See https://github.com/systemd/systemd/pull/1534#commitcomment-13744013

Actually, thinking about this, maybe it would be nicer to actually look
for "Limit" in the string rather than chopping off a "Default"....
Sounds more generic...

src/shared/bus-util.c

@@ -2163,7 +2163,7 @@ int bus_property_get_rlimit(
                 struct rlimit buf = {};
                 int z;
 
-                z = rlimit_from_string(startswith(property, "Default") ? property + 7 : property);
+                z = rlimit_from_string(strstr(property, "Limit"));
                 assert(z >= 0);
 
                 getrlimit(z, &buf);