Avoid duplicates

src/zeronetavahi

@@ -134,10 +134,13 @@ while IFS='' read -r line || [[ -n "$line" ]]; do
     if [ ${state} -eq "1" ]; then
         if [[ $line == *"address ="* ]]; then
             address=$(echo $line | awk -F '[' '{print $2}' | awk -F ']' '{print $1}')
-            echo "    http://$peer:$TRACKER_PORT/announce" >> $ZERONET_CONFIG.new
-            state=0
+            tracker_url="http://$peer:$TRACKER_PORT/announce"
+            if ! grep -q "$tracker_url" $ZERONET_CONFIG.new; then
+                echo "    $tracker_url" >> $ZERONET_CONFIG.new
                 tracker_ctr=$((tracker_ctr + 1))
             fi
+            state=0
+        fi
     fi
     if [[ $line == *"hostname ="* ]]; then
         peer=$(echo $line | awk -F '[' '{print $2}' | awk -F ']' '{print $1}')