Central point architecture support for GTP

The central point architecture is enhanced to address the GTP-C message rate-limiting to protect GGSN from GTP-C message flood and to distribute GTP-U traffic handled by a GGSN and SGSN pair on all SPUs by switching to tunnel endpoint identifier (TEID)-based hash distribution. Previously, the GTP ALG used to drop incoming GTP-C packets if the GGSN or SGSN direction was not determined. Now, to prevent GTP-C packets from being dropped, a new flow session is created and the GTP-C traffic is allowed to pass even if the GGSN or SGSN direction is not determined. Later, the GGSN IP can be determined using the correct SPU to create the flow session, and the session must be migrated to the designated SPU.