Add: adding entrypoint to ext-dn
This merge request aims to bring additional configuration to the ext-dn that we needed in our setup. Indeed, in this MR:
- We first disable the TCP checksum,
- We setup an MTU around 1460 in order to feet the 1500 octets when the packet coming from the DN is encapsulated within GTP header,
- Add a route to the UE,
- Remote the use of the interface N3,
- Add SNAT rule in order to allow traffic coming from UE to reach the outside world.