new header file: cpc_gre.h added
added GRE4 and GRE6 to pkt_types_gen.py, also corrected a bug for GTPU4 and GTPU6
pkt_types_gen.py => clean-up on GTPU related push_transitions
c_types_pkt_classifier => GRE related functions implemented
c_types_pkt_classifier => GRE related functions implemented, including pop_gre()
gnu_linux driver => implemented GRE related functions
added GRE extensions to translation utilities for OF12 and OF13
c_types_pktclassifier => changes to push_gre() and pop_gre() functions
c_types_pktclassifier.c => corrected bug in function push_gre() => invalid payload length calculation
c_types_pktclassifier.c => corrected bug in function push_gre() => invalid payload length calculation
c_types_pktclassifier.c => corrected bug in function push_gre() => do not use ident from IPv4 headers, as there may be Ethernet frames that are not IPv4
cpc_gre.h => suppress reading of GRE key and seqno, if flags are not present
cpc_gre.h => fixed flexible occurence of CSUM, KEY, SEQNO
added checksum calculation for GRE to file packet_proto_meta_imp.h
cpc_gre.h => fixed bug in checksum calculations => do not construct an IP pseudo header, as it is not used in the GRE checksum calculation
cpc_gre.h => renamed constant GRE_PROT_TYPE_TRANSPARENT_ETHERNET_BRIDGING