GTP-u graph node for the CNET networking stack

[KeithWiles]

Difficulty: Fairly hard as one needs to learn CNDP graph node library and GTP-u protocol.

Description:
GTP-u graph node for CNET a CNDP graph node-based network stack (IPv4/UDP/TCP)

• Create and test a GTP-u graph node for the CNET stack. CNET stack has a stub version for a starting point cndp/lib/cnet/gtpu.
• Graph Node library source and documentation.
  • The graph node library was taken from DPDK with minor changes to work within CNDP.
• GTP-u graph node needs to comply to GTP-u protocol.
• Needs to be tested and verified it works with the CNET stack.
• This one can be fairly complex as one needs to learn the graph node library and the GTP-u protocol.

TODO: Add more information.

[maryamtahhan]

GTP-U uses UDP as a transport, so from a graph POV anything with a DST UDP address of 2152 should get filtered to the GTP-U node(s), there's some more useful info here also https://www.etsi.org/deliver/etsi_ts/129200_129299/129281/08.00.00_60/ts_129281v080000p.pdf re header format and what not...
We may want to consider a separate encap and decap node as they may sit in different points of the graph