pnf_nr_p7_pack_and_send_p7_message(): don't use global buffer

This function packs P7 messages. At least RX_data.indication messages
might be much bigger than the global buffer that is used here. Allocate
the buffer on the stack, and make it bigger. Do not use the global
buffer, it's simply not necessary; increasing the global tx buffer size
might have negative effects elsewhere in the code.

That change might make the function reentrant. The mutex seems to only
guards the codec config. However, leave it to not introduce any
regressions as of now.

nfapi/open-nFAPI/pnf/src/pnf_p7.c

@@ -579,8 +579,8 @@ int pnf_nr_p7_pack_and_send_p7_message(pnf_p7_t* pnf_p7, nfapi_nr_p7_message_hea
     return -1;
   }
 
-  int len =
-      nfapi_nr_p7_message_pack(header, pnf_p7->tx_message_buffer, sizeof(pnf_p7->tx_message_buffer), &pnf_p7->_public.codec_config);
+  uint8_t tx_buf[131072]; // four times NFAPI_MAX_PACKED_MESSAGE_SIZE as of this commit
+  int len = nfapi_nr_p7_message_pack(header, tx_buf, sizeof(tx_buf), &pnf_p7->_public.codec_config);
 
   if (len < 0) {
     if (pthread_mutex_unlock(&(pnf_p7->pack_mutex)) != 0) {
@@ -611,7 +611,7 @@ int pnf_nr_p7_pack_and_send_p7_message(pnf_p7_t* pnf_p7, nfapi_nr_p7_message_hea
       uint16_t segment_size = size + NFAPI_NR_P7_HEADER_LENGTH;
 
       // Update the header with the m and segement
-      memcpy(&buffer[0], pnf_p7->tx_message_buffer, NFAPI_NR_P7_HEADER_LENGTH);
+      memcpy(&buffer[0], tx_buf, NFAPI_NR_P7_HEADER_LENGTH);
 
       // set the segment length
       buffer[6] = (segment_size & 0xFF00) >> 8;
@@ -620,7 +620,7 @@ int pnf_nr_p7_pack_and_send_p7_message(pnf_p7_t* pnf_p7, nfapi_nr_p7_message_hea
       // set the m & segment number
       buffer[8] = ((!last) << 7) + segment;
 
-      memcpy(&buffer[NFAPI_NR_P7_HEADER_LENGTH], pnf_p7->tx_message_buffer + offset, size);
+      memcpy(&buffer[NFAPI_NR_P7_HEADER_LENGTH], tx_buf + offset, size);
       offset += size;
 
       if (pnf_p7->_public.checksum_enabled) {
@@ -631,11 +631,11 @@ int pnf_nr_p7_pack_and_send_p7_message(pnf_p7_t* pnf_p7, nfapi_nr_p7_message_hea
     }
   } else {
     if (pnf_p7->_public.checksum_enabled) {
-      nfapi_nr_p7_update_checksum(pnf_p7->tx_message_buffer, len);
+      nfapi_nr_p7_update_checksum(tx_buf, len);
     }
 
     // simple case that the message fits in a single segment
-    pnf_p7_send_message(pnf_p7, pnf_p7->tx_message_buffer, len);
+    pnf_p7_send_message(pnf_p7, tx_buf, len);
   }
 
   pnf_p7->sequence_number++;