Provide peek_nr_nfapi_p7_sfn_slot() for fast msg dec

The next commits refactor the rx handling of messages in the PNF. To
efficiently handle them, provide a "peek()" function that gives us the
frame/slot for which a message is destined. This allows to decide if a
message is on time and select a destination buffer, before unpacking it
completely, avoiding copies.

nfapi/open-nFAPI/nfapi/public_inc/nfapi_nr_interface.h

@@ -10,6 +10,8 @@
 #define _NFAPI_NR_INTERFACE_H_
 #include "nfapi_common_interface.h"
 
+#include <stdbool.h>
+
 #define NFAPI_NR_P5_HEADER_LENGTH 10
 #define NFAPI_NR_P7_HEADER_LENGTH 18
 
@@ -177,6 +179,18 @@ int nfapi_nr_p7_message_unpack(void *pMessageBuf,
                                uint32_t unpackedBufLen,
                                nfapi_p7_codec_config_t *config);
 
+/*! \brief Peeks the SFN and Slot of an (n)FAPI P7 message
+ *  \param pMessageBuf A pointer to an encoded P7 message header
+ *  \param messageBufLen The size of the encoded P7 message header
+ *  \param SFN A pointer to store the peeked SFN
+ *  \param Slot A pointer to store the peeked Slot
+ *  \return true on success, false, otherwise.
+ *
+ * The function will decode the encoded SFN and Slot from an encoded P7 (n)FAPI message
+
+ */
+bool peek_nr_nfapi_p7_sfn_slot(void *pMessageBuf, uint32_t messageBufLen, uint16_t *SFN, uint16_t *Slot);
+
 /*! \brief Calculates the checksum of a  message
  *
  *  \param buffer Pointer to the packed message

nfapi/open-nFAPI/nfapi/src/nfapi_p7.c

@@ -6202,6 +6202,18 @@ int nfapi_p7_message_unpack(void *pMessageBuf,
     return 0;
 }
 
+bool peek_nr_nfapi_p7_sfn_slot(void *pMessageBuf, uint32_t messageBufLen, uint16_t *SFN, uint16_t *Slot)
+{
+  uint8_t *pReadPackedMessage = &((uint8_t *)pMessageBuf)[NFAPI_NR_P7_HEADER_LENGTH];
+  uint8_t *end = (uint8_t*)pMessageBuf + messageBufLen;
+  if(!(pull16(&pReadPackedMessage, SFN, end) && pull16(&pReadPackedMessage, Slot, end))) {
+    NFAPI_TRACE(NFAPI_TRACE_ERROR, "Failed to peek SFN.Slot\n");
+    return false;
+  }
+  NFAPI_TRACE(NFAPI_TRACE_DEBUG, "Peeked SFN.Slot is (%d.%d)\n", *SFN, *Slot);
+  return true;
+}
+
 int nfapi_nr_p7_message_unpack(void *pMessageBuf,
                                uint32_t messageBufLen,
                                void *pUnpackedBuf,

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

@@ -28,6 +28,7 @@
 #include <stdio.h>
 
 #include "pnf_p7.h"
+#include "nr_fapi_p7_utils.h" // for 5G/NR message utils
 
 #define FAPI2_IP_DSCP	0