Only send data if interface is running

If the macnocker client tries to send data, but the interface is not running,
this will result in error messages. However, an interface being down is a
valid state and should not result in error messages. So first check the current
state of the interface before trying to send data.

Fixes: #104
Signed-off-by: Fabian Bläse <fabian@blaese.de>
Acked-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

macnockclient.c

@@ -86,6 +86,19 @@ void macNockClient_run()
     {
         log_trace("[c] sending\n");
 
+        // check if bound interface is down, trying to send data would result in an error
+        if (!(ioctl(fd, SIOCGIFFLAGS, &ifr) == 0))
+        {
+            perror("[c] ERROR: Can't read Interface information");
+            goto retry;
+        }
+        if (!(ifr.ifr_flags & IFF_RUNNING))
+        {
+            // interface is not running, silently ignore
+            log_debug("[c] interface is not running\n");
+            goto retry;
+        }
+
         int sent = sendto(fd, nock, len, 0, (struct sockaddr *)&servaddr, sizeof(servaddr));
         if (sent == -1)
         {
@@ -96,6 +109,7 @@ void macNockClient_run()
             perror("[c] ERROR: Can't send all data");
         }
 
+retry:
         usleep(1 * 1000 * 1000); // sleep 1 s
     }