gnrc_netif: 6lo.h: add flags to indicate SRF capability

sys/include/net/gnrc/netif/6lo.h

@@ -18,12 +18,34 @@
 #ifndef NET_GNRC_NETIF_6LO_H
 #define NET_GNRC_NETIF_6LO_H
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+/**
+ * @name    Local 6LoWPAN capability flags
+ * @anchor  net_gnrc_netif_6lo_local_flags
+ * @see     gnrc_netif_6lo_t::local_flags
+ *
+ * Like the the capability flags in the [6LoWPAN Capability Indication Option
+ * (6CIO)](https://tools.ietf.org/html/rfc7400#section-3.3) are less about
+ * hardware capabilities than about the implementation status within the
+ * network. For the flags in this group it is currently undefined how to
+ * exchange the capabilities between nodes, but they might be added to the 6CIO
+ * at a later point. Once the 6CIO is implemented in GNRC and the flag is
+ * supported by it, the corresponding flag in these local flags can be removed.
+ * @{
+ */
+/**
+ * @brief   Selective Fragment Recovery enabled
+ * @see     [RFC 8931](https://tools.ietf.org/html/rfc8931)
+ */
+#define GNRC_NETIF_6LO_LOCAL_FLAGS_SFR  (0x01)
+/** @} */
+
 /**
  * @brief   6Lo component of @ref gnrc_netif_t
  */
@@ -35,6 +57,15 @@ typedef struct {
      *          @ref net_gnrc_sixlowpan_frag "gnrc_sixlowpan_frag".
      */
     uint16_t max_frag_size;
+    /**
+     * @brief   6LoWPAN capability flags beyond the ones advertised in
+     *          [6LoWPAN Capability Indication Option
+     *          (6CIO)](https://tools.ietf.org/html/rfc7400#section-3.3)
+     *
+     * @see     [Local 6LoWPAN capability flags](@ref
+     *          net_gnrc_netif_6lo_local_flags)
+     */
+    uint8_t local_flags;
 } gnrc_netif_6lo_t;
 
 #ifdef __cplusplus