Reset CU-UP E1 UE contexts after E1 Setup Response

38.463 sec. 8.2.3 says

> This procedure also re-initialises the E1AP UE-related contexts (if
> any) and erases all related signalling connections in the two nodes like
> a Reset procedure would do.

Hence, delete all contexts after reception of E1 Setup Response. This
minimizes a risk of receiving an E1 bearer setup req for an existing UE,
which currently leads to an assert [we trust the CU-CP does not send the
same UE ID twice, as we only "mirror" the existing UE ID].

openair2/E1AP/e1ap.c

@@ -219,6 +219,8 @@ int e1apCUUP_handle_SETUP_RESPONSE(sctp_assoc_t assoc_id, e1ap_upcp_inst_t *inst
     return -1;
   }
   free_e1ap_cuup_setup_response(&out);
+
+  e1_reset(); // reset all UE contexts, if any: see 38.463 sec 8.2.3
   return 0;
 }