Based on the search results, I found that OpenWRT has a package called tcp-port-used which provides a simple Node.js module to check if a TCP port is already bound.

You can install this package using the following command:

opkg install tcp-port-used

Once installed, you can use the tcpportused command to check if a port is in use. For example:

tcpportused 8080

This will return 1 if the port is in use and 0 otherwise.

Note that this package is available on the OpenWRT package repository, so you can easily install it on your device.