[Boot DIP options]

would check routing table on boot. Because you are stating that you are getting internet connection from eth0... as far as i know pine runs a DHCP server on boot on eth0 with no real default gateway.

side note: why would you enable wlan1 ? If you are getting a internet connection from eth0 ?

[MITM on another network]

Well when you are not the router of that network you are going to have to spam and i mean really spam that your mac is the gateway's ip. Then the clients will send there packets directed to the gateway's ip to you.

Think that will get you there.