GTPv2-C sequence number overflows at the incorrect value

[radoslav-georgiev-flolive]

The sequence number counter should wrap around to zero on reaching 0x800000 instead of 0x1000000. The explanation why this value should be used can be found in 3GPP TS 29.274, section 7.6 ("Reliable Delivery of Signalling Messages"), where it is mentioned that sequence numbers with their most significant bit set to 1 should be used only for Command messages and for requests which were triggered by Command messages, as well as for Triggered Reply messages, and not for requests which were not triggered by a Command message (i.e. Initial Request messages). It is therefore assumed that if the sequence number counter is initialized with zero, it is supposed to be used when sending Initial Request messages only. That's why its value becoming 0x800000 (and being incremented further) would in practice change the type of the message and the way it's supposed to be handled, which is incorrect behavior.