log an error when failing to go into nonblocking mode

nethogs.cpp

@@ -346,10 +346,13 @@ int main (int argc, char** argv)
 		{
 			/* The following code solves sf.net bug 1019381, but is only available
 			 * in newer versions (from 0.8 it seems) of libpcap 
+			 *
+			 * update: version 0.7.2, which is in debian stable now, should be ok
+			 * also. 
 			 */
 			if (dp_setnonblock (newhandle, 1, errbuf) == -1)
 			{
-			  // ERROR
+				fprintf(stderr, "Error putting libpcap in nonblocking mode\n");
 			}
 			handles = new handle (newhandle, current_dev->name, handles);
 		}