Refactors the GRE node to work with both IPv4 and IPv6 transports.
Note that this changes the binary configuration API to support both
address families; each address uses the same memory for either
address type and a flag to indicate which is in use.
The CLI and VAT syntax remains unchanged; the code detects whether
an IPv4 or an IPv6 address was given.
Configuration examples:
IPv4 CLI: create gre tunnel src 192.168.1.1 dst 192.168.1.2
IPv6 CLI: create gre tunnel src 2620:124:9000::1 dst 2620:124:9000::2
IPv4 VAT: gre_add_del_tunnel src 192.168.1.1 dst 192.168.1.2
IPv6 VAT: gre_add_del_tunnel src 2620:124:9000::1 dst 2620:124:9000::2
Change-Id: Ica8ee775dc101047fb8cd41617ddc8fafc2741b0
Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
