netopt: add NETOPT_PDU_SIZE

sys/include/net/netopt.h

@@ -195,6 +195,22 @@ typedef enum {
      * @brief   (uint16_t) maximum protocol data unit
      */
     NETOPT_MAX_PDU_SIZE,
+    /**
+     * @brief   (uint16_t) protocol data unit size
+     *
+     * When set, fixes the number of bytes to be received. This is required for
+     * MAC layers with implicit header mode (no packet length information in
+     * PDDU) and predictable packet length (e.g LoRaWAN beacons). The device
+     * driver implementation should attempt to read exactly the expected number
+     * of bytes (possibly filling it up with garbage data if the payload is
+     * smaller).
+     *
+     * When get, returns the number of expected bytes for the next reception.
+     *
+     * In some MAC layers it will only be effective if used in conjunction with
+     * @ref NETOPT_FIXED_HEADER
+     */
+    NETOPT_PDU_SIZE,
     /**
      * @brief   (@ref netopt_enable_t) frame preloading
      *

sys/net/crosslayer/netopt/netopt.c

@@ -41,6 +41,7 @@ static const char *_netopt_strmap[] = {
     [NETOPT_IPV6_FORWARDING]       = "NETOPT_IPV6_FORWARDING",
     [NETOPT_IPV6_SND_RTR_ADV]      = "NETOPT_IPV6_SND_RTR_ADV",
     [NETOPT_TX_POWER]              = "NETOPT_TX_POWER",
+    [NETOPT_PDU_SIZE]              = "NETOPT_PDU_SIZE",
     [NETOPT_MAX_PDU_SIZE]          = "NETOPT_MAX_PDU_SIZE",
     [NETOPT_PRELOADING]            = "NETOPT_PRELOADING",
     [NETOPT_PROMISCUOUSMODE]       = "NETOPT_PROMISCUOUSMODE",