app/testpmd: add GRE key for raw encap/decap
app/testpmd: add GRE key for raw encap/decap

GRE key (rte_flow_item_type_gre_key) is also needed in
raw encapsulation/decapsulation.

Signed-off-by: Xiaoyu Min <03352a7947822e04037757091119acfbe3910106@mellanox.com>
Reviewed-by: Ferruh Yigit <ba8734c3c506d2e3557bd4ac8fdaccd25bdb9aa7@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk