Prevent the PNF from sending P7 messages after sending a STOP.indication

Upon stopping the PNF, when sending the STOP.indication to the VNF, set pnf_p7->terminate to 1.

Add a check on the PNF P7 send functions to not send a message after pnf_p7->terminate is set

nfapi/oai_integration/socket/socket_pnf.c

@@ -78,6 +78,10 @@ static int send_p7_msg(pnf_p7_t *pnf_p7, uint8_t *msg, uint32_t len)
 
 bool pnf_nr_send_p7_message(pnf_p7_t *pnf_p7, nfapi_nr_p7_message_header_t *header, uint32_t msg_len)
 {
+  if (pnf_p7->terminate) {
+    //don't send any further P7 messages after terminating
+    return false;
+  }
   header->m_segment_sequence = NFAPI_NR_P7_SET_MSS(0, 0, pnf_p7->sequence_number);
 
   // Need to guard against different threads calling the encode function at the same time