[GTP] Incorrect destination TEID=0 (#3043)

If eg. PCRF or AAA diameter link is not yet ready (eg. PCRF crashed),
and a client sends a CreateSessionRequest announcing its ow F-TEID,
then open5gs-smfd answers with Create Session Response Cause=
"Remote peer not responding", but it is not setting the received F-TEID
in the header of the response, instead it sends with TEI=0.

As a result, the peer cannot match the CreateSessionResponse,
and needs to rely on its own timeout timer to figure out
that specific request failed.

To address this issue, I modified the GTP Response message to check
the Sender F-TEID and send it accordingly, setting the destination TEID
to the value of the Sender F-TEID.

I've made this modification only for SMF, but MME and SGW-C have not done so;
if you need to, you can work from the examples in SMF.

Similarly, the same situation can happen with PFCP. If anyone needs to do this
in the future, I think you can work on it this way.

docs/_docs/guide/01-quickstart.md

@@ -233,7 +233,7 @@ MME-frDi  = 127.0.0.2 :3868 for S6a
 SGWC-gtpc = 127.0.0.3 :2123 for S11
 SGWC-pfcp = 127.0.0.3 :8805 for Sxa
 
-SMF-gtpc  = 127.0.0.4 :2123 for S5c, N11
+SMF-gtpc  = 127.0.0.4 :2123 for S5c
 SMF-gtpu  = 127.0.0.4 :2152 for N4u (Sxu)
 SMF-pfcp  = 127.0.0.4 :8805 for N4 (Sxb)
 SMF-frDi  = 127.0.0.4 :3868 for Gx auth