Avoid duplicates

src/zeronetavahi

@@ -134,9 +134,12 @@ 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" >> $ZERONET_CONFIG.new
+            tracker_url="http://$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
-            tracker_ctr=$((tracker_ctr + 1))
         fi
     fi
     if [[ $line == *"hostname ="* ]]; then