Fix DLNA port, and expose them in Docker

Signed-off-by: Andrew DeMaria <lostonamountain@gmail.com>

install/docker/Dockerfile

@@ -3,7 +3,7 @@ FROM alpine:3.9
 LABEL description="Airsonic is a free, web-based media streamer, providing ubiquitious access to your music." \
       url="https://github.com/airsonic/airsonic"
 
-ENV AIRSONIC_PORT=4040 AIRSONIC_DIR=/airsonic CONTEXT_PATH=/
+ENV AIRSONIC_PORT=4040 AIRSONIC_DIR=/airsonic CONTEXT_PATH=/ UPNP_PORT=4041
 
 WORKDIR $AIRSONIC_DIR
 
@@ -27,6 +27,10 @@ COPY target/dependency/airsonic-main.war airsonic.war
 
 EXPOSE $AIRSONIC_PORT
 
+# Default DLNA/UPnP ports
+EXPOSE $UPNP_PORT
+EXPOSE 1900/udp
+
 VOLUME $AIRSONIC_DIR/data $AIRSONIC_DIR/music $AIRSONIC_DIR/playlists $AIRSONIC_DIR/podcasts
 
 HEALTHCHECK --interval=15s --timeout=3s CMD wget -q http://localhost:"$AIRSONIC_PORT""$CONTEXT_PATH"rest/ping -O /dev/null || exit 1