drivers/slipdev: report NETOPT_ADDRESS to simulate l2 address

A lot of things break if `GNRC_NETIF_FLAGS_HAS_L2ADDR` is not set.
In order to handle router advertisements and auto-configureation,
generate a faux l2 address based on the netdev ID.

drivers/slipdev/Makefile.dep

@@ -1,4 +1,5 @@
 USEMODULE += tsrb
+USEMODULE += eui_provider
 FEATURES_REQUIRED += periph_uart
 
 ifneq (,$(filter slipdev_stdio,$(USEMODULE)))

drivers/slipdev/slipdev.c

@@ -21,6 +21,7 @@
 #include "log.h"
 #include "slipdev.h"
 #include "slipdev_internal.h"
+#include "net/eui_provider.h"
 
 /* XXX: BE CAREFUL ABOUT USING OUTPUT WITH MODULE_SLIPDEV_STDIO IN SENDING
  * FUNCTIONALITY! MIGHT CAUSE DEADLOCK!!!1!! */
@@ -231,6 +232,12 @@ static int _get(netdev_t *netdev, netopt_t opt, void *value, size_t max_len)
             assert(max_len == sizeof(uint16_t));
             *((uint16_t *)value) = NETDEV_TYPE_SLIP;
             return sizeof(uint16_t);
+#if IS_USED(MODULE_SLIPDEV_L2ADDR)
+        case NETOPT_ADDRESS_LONG:
+            assert(max_len == sizeof(eui64_t));
+            netdev_eui64_get(netdev, value);
+            return sizeof(eui64_t);
+#endif
         default:
             return -ENOTSUP;
     }

makefiles/pseudomodules.inc.mk

@@ -128,6 +128,7 @@ PSEUDOMODULES += sched_cb
 PSEUDOMODULES += semtech_loramac_rx
 PSEUDOMODULES += shell_hooks
 PSEUDOMODULES += slipdev_stdio
+PSEUDOMODULES += slipdev_l2addr
 PSEUDOMODULES += sock
 PSEUDOMODULES += sock_async
 PSEUDOMODULES += sock_aux_local

sys/include/net/gnrc/netif/conf.h

@@ -143,7 +143,7 @@ extern "C" {
  *       address types are included
  */
 #ifndef GNRC_NETIF_L2ADDR_MAXLEN
-#if defined(MODULE_NETDEV_IEEE802154) || defined(MODULE_XBEE)
+#if defined(MODULE_NETDEV_IEEE802154) || defined(MODULE_XBEE) || defined(MODULE_SLIPDEV_L2ADDR)
 #define GNRC_NETIF_L2ADDR_MAXLEN   (IEEE802154_LONG_ADDRESS_LEN)
 #elif   MODULE_NETDEV_ETH
 #define GNRC_NETIF_L2ADDR_MAXLEN   (ETHERNET_ADDR_LEN)

sys/net/gnrc/netif/gnrc_netif.c

@@ -1364,8 +1364,13 @@ static void _test_options(gnrc_netif_t *netif)
             assert(netif->flags & GNRC_NETIF_FLAGS_HAS_L2ADDR);
             assert(netif->l2addr_len >= 3U && netif->l2addr_len <= 5U);
             break;
-        case NETDEV_TYPE_LORA: /* LoRa doesn't provide L2 ADDR */
         case NETDEV_TYPE_SLIP:
+#if IS_USED(MODULE_SLIPDEV_L2ADDR)
+            assert(netif->flags & GNRC_NETIF_FLAGS_HAS_L2ADDR);
+            assert(8U == netif->l2addr_len);
+            break;
+#endif /* IS_USED(MODULE_SLIPDEV_L2ADDR) */
+        case NETDEV_TYPE_LORA: /* LoRa doesn't provide L2 ADDR */
             assert(!(netif->flags & GNRC_NETIF_FLAGS_HAS_L2ADDR));
             assert(0U == netif->l2addr_len);
             /* don't check MTU here for now since I'm not sure the current

sys/net/gnrc/netif/gnrc_netif_device_type.c

@@ -56,6 +56,11 @@ netopt_t gnrc_netif_get_l2addr_opt(const gnrc_netif_t *netif)
                 }
             }
             break;
+#endif
+#if defined(MODULE_SLIPDEV_L2ADDR)
+        case NETDEV_TYPE_SLIP:
+            res = NETOPT_ADDRESS_LONG;
+            break;
 #endif
         default:
             break;

sys/net/link_layer/l2util/l2util.c

@@ -123,6 +123,11 @@ int l2util_eui64_from_addr(int dev_type, const uint8_t *addr, size_t addr_len,
                 return -EINVAL;
             }
 #endif /* defined (MODULE_NRF24L01P_NG) */
+#if defined(MODULE_SLIPDEV_L2ADDR)
+        case NETDEV_TYPE_SLIP:
+            memcpy(eui64, addr, addr_len);
+            return sizeof(eui64_t);
+#endif /* defined(MODULE_SLIPDEV_L2ADDR) */
         default:
             (void)addr;
             (void)addr_len;
@@ -230,6 +235,11 @@ int l2util_ipv6_iid_to_addr(int dev_type, const eui64_t *iid, uint8_t *addr)
             memcpy(&addr[addr_len - 3], &iid->uint8[5], 3);
             return addr_len;
 #endif /* defined(MODULE_NRF24L01P_NG) */
+#if defined(MODULE_SLIPDEV_L2ADDR)
+        case NETDEV_TYPE_SLIP:
+            memcpy(addr, iid, sizeof(eui64_t));
+            return sizeof(eui64_t);
+#endif /* defined(MODULE_SLIP) */
         default:
             (void)iid;
             (void)addr;
@@ -288,6 +298,10 @@ int l2util_ndp_addr_len_from_l2ao(int dev_type,
             (void)opt;
             return 5; /* maximum length */
 #endif /* defined(MODULE_NRF24L01P_NG) */
+#if defined(MODULE_SLIPDEV_L2ADDR)
+        case NETDEV_TYPE_SLIP:
+            return sizeof(eui64_t);
+#endif /* defined(MODULE_SLIPDEV_L2ADDR) */
         default:
             (void)opt;
 #ifdef DEVELHELP