GTPv2 vs GTPv1 Header

There is no major difference between v1 and v2 header apart from introducing the new fields in v2 and the removal of Extension-header, Flags for Sequence number and N-PDU.

* Piggy backing Flag - When this flag is set in create session response then it means there is a create bearer request which is piggybacked in the same GTP message.
*Since GTPv2-C is designed for Control, there is no need to have a N-PDU which is required during Inter RAT RAU.
Hence strip that.
* TEID need not be present in the case of GTP Echo messages. So this is stripped in v2.
*Sequence number field is mandatory in V2.

+	Bit 0-2			3	4	5-7			8-15								16-23								24-31
0	Version			Piggybacking flag (P)	TEID flag (T)	Spare			Message Type								Total length
32	TEID (only present if T=1)
64 (32 if TEID not present)	Sequence number																Spare