It allows for much better control on the lifecycle of the session, and
already shows some missing tear down paths in case of errors.
It also clarifies the existence of "sess" pointer in several paths.
The code also becomes clearer overall, since all the transitions and
logic to send next messages are put together.
Tear down of the session will be integrated into gsm-sm in a follow-up
patch.
The 5gc session setup is only partially moved to gsm-sm, and left as an
exercise for users wishin to improve 5gc support.
In the past only GTPv2C was supported, and had the "gtp" generic prefix.
Later on, GTPv1C support was added, and "gtp1" prefix was used.
Let's move GTPv2C specific bits to have "gtp2" prefix too, and leave
"gtp" prefix for generic stuff among different GTP versions.
Pau Espin
Sukchan Lee