Handle SIOCGIFMEDIA in the ioctl shim

Vivox's network reachability provider calls SIOCGIFMEDIA for each interface and drops every interface whose ioctl fails. Darling passed the Darwin request through to Linux, which returns ENOTTY, so the SDK saw no usable interface and vx_req_connector_create failed with 1004. Return a synthetic active Ethernet/IEEE802.11 media record built from the host SIOCGIFFLAGS result, and add a standalone probe that fails on the old behavior.

tools/riot-ifmedia-check.c

@@ -0,0 +1,58 @@
+// Vivox's network reachability provider calls SIOCGIFMEDIA on each interface
+// and drops every interface whose ioctl fails. Darling used to pass the Darwin
+// request through to Linux, which returns ENOTTY.
+#include <ifaddrs.h>
+#include <net/if.h>
+#include <net/if_media.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <sys/sockio.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+static int check(const char *name, int required) {
+    int sock = socket(AF_INET, SOCK_DGRAM, 0);
+    struct ifmediareq ifmr;
+    memset(&ifmr, 0, sizeof(ifmr));
+    strncpy(ifmr.ifm_name, name, sizeof(ifmr.ifm_name) - 1);
+    errno = 0;
+    int rc = ioctl(sock, SIOCGIFMEDIA, &ifmr);
+    close(sock);
+    int active = (ifmr.ifm_status & (IFM_AVALID | IFM_ACTIVE)) == (IFM_AVALID | IFM_ACTIVE);
+    int known_type = IFM_TYPE(ifmr.ifm_current) == IFM_ETHER ||
+                     IFM_TYPE(ifmr.ifm_current) == IFM_IEEE80211;
+    printf("IFMEDIA interface=%s rc=%d errno=%d current=0x%x status=0x%x active=%d type=%d\n",
+           name, rc, errno, ifmr.ifm_current, ifmr.ifm_status, active, known_type);
+    if (rc != 0) return required;
+    return required && (!active || !known_type);
+}
+
+int main(int argc, char **argv) {
+    int failures = 0;
+    if (argc > 1) {
+        for (int i = 1; i < argc; i++) failures += check(argv[i], 1);
+    } else {
+        struct ifaddrs *interfaces = NULL;
+        char name[IFNAMSIZ] = {0};
+        if (getifaddrs(&interfaces) != 0) {
+            printf("IFMEDIA getifaddrs failed errno=%d\n", errno);
+            return 1;
+        }
+        for (struct ifaddrs *entry = interfaces; entry; entry = entry->ifa_next) {
+            if (!entry->ifa_addr || entry->ifa_addr->sa_family != AF_INET) continue;
+            if (entry->ifa_flags & IFF_LOOPBACK) continue;
+            strncpy(name, entry->ifa_name, sizeof(name) - 1);
+            break;
+        }
+        freeifaddrs(interfaces);
+        if (!name[0]) {
+            printf("IFMEDIA no non-loopback IPv4 interface\n");
+            return 1;
+        }
+        failures += check(name, 1);
+    }
+    printf("IFMEDIA_CHECK failures=%d\n", failures);
+    return failures ? 1 : 0;
+}