bandwhich
Terminal bandwidth utilization tool
... on linux, or you can install it via rustup. Cargo installs bandwhich to ~/.cargo/bin/bandwhich but you need root priviliges to run bandwhich. To install bandwhich on OpenWRT, you'll need to compile a binary that would fit its processor architecture. This might mean you would have to cross compile if, for example, you're working on an x86_64 and the OpenWRT is installed on an arm7.