Adapt xdpd for DPDK 1.7

In DPDK 1.7, Poll Mode Drivers (PMD) register from static
constructors and there is no rte_pmd_init_all() function anymore.
rte_eal_pci_probe() has also become optional.
In order for PMDs to register, their archive must be force-included
in the xdpd binary, which is achieved with --whole-archive linker
flag.

Signed-off-by: David Verbeiren <david.verbeiren@intel.com>
Merge remote-tracking branch 'origin/devel0.6/dpdk1.7' into devel-0.6
Updating documentation
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
added file cpc_gre.h for gnu_linux_dpdk