[Docker] Fix: Bind socat to the right port

tools/docker-entrypoint.sh

@@ -10,8 +10,9 @@ if [ "$EXPOSE_TCP" == "true" ]; then
     while read -r i; do if [ "$i" = "lightning-rpc" ]; then break; fi; done \
     < <(inotifywait  -e create,open --format '%f' --quiet "$LIGHTNINGD_DATA" --monitor)
     echo "C-Lightning started"
+    echo "C-Lightning started, RPC available on port $LIGHTNINGD_RPC_PORT"
 
-    socat "TCP4-listen:$LIGHTNINGD_PORT,fork,reuseaddr" "UNIX-CONNECT:$LIGHTNINGD_DATA/lightning-rpc" &
+    socat "TCP4-listen:$LIGHTNINGD_RPC_PORT,fork,reuseaddr" "UNIX-CONNECT:$LIGHTNINGD_DATA/lightning-rpc" &
     fg %-
 else
     lightningd "$@"