Use UL NAS Count to derive KgNB (6.8 of 3GPP TS 33.501)

The UE shall use the currently stored UL NAS count to derive the
KgNB. Hardcoding the UL count to 0 is wrong, if there is a reset
to be done it should be explicitly done elsewhere.

Closes #832

openair3/NAS/NR_UE/nr_nas_msg.c

@@ -510,7 +510,7 @@ static void derive_ue_keys(uint8_t *buf, nr_ue_nas_t *nas)
   derive_kausf(ck, ik, sqn, kausf, nas->uicc);
   derive_kseaf(kausf, kseaf, nas->uicc);
   derive_kamf(kseaf, kamf, 0x0000, nas->uicc);
-  derive_kgnb(kamf, 0, kgnb);
+  derive_kgnb(kamf, nas->security.nas_count_ul, kgnb);
 
   printf("kausf:");
   for (int i = 0; i < 32; i++) {