Enable IP TUN interface configuration upon reception of PDU Session Establishment Accept NAS message

-User plane traffic validation with OAI UE and OAI CN:

-Downlink ping initiated from the CN is received at the IP interface of the UE. However it seems that there is some packet corruption preventing the generaration of ping reply.

-Uplink ping initiated from the UE reaches the OAI CN machine. However no ping reply is seen yet either.