l3-longevity: Report avg latency for endpoints on a particular port.

Use endpoint EID to match Port EID so we can know which ports
endpoints belong to.

Signed-off-by: Ben Greear <greearb@candelatech.com>

py-json/l3_cxprofile.py

@@ -542,6 +542,8 @@ class L3CXProfile(LFCliBase):
 
         self.local_realm.wait_until_cxs_appear(these_cx, debug=debug_)
 
+        return these_cx, these_endp
+
     def to_string(self):
         pprint.pprint(self)