You can do this by executing these UCI commands:
uci set network.lan.ifname='eth0'
service network reload
uci commit network
service network reload && /etc/init.d/adb stop && /etc/init.d/adb disable
After these, your USB should not give any network. If you wish to gain your Micro-USB functionality back you will have to activate everything back again with other services like SMS utilities or Json-RPC.