here is an example to share data connection with WP76/WP77 ECM interface
You might change the ecm interface to eth0 interface.
The example above is using NAT, so it is using private IP instead of the external IP address you obtained.
I guess you might need to study some bridge command in linux if you want the eth0 to use the external IP address.
“Mobile Broadband adapter Cellular 2” is directly accessing the RMNET interface of module, so it is different from eth0.