mbuf: add fields for tunnels

mbuf: add fields for tunnels

Replace the "reserved2" field with the "packet_type" field
and add the "inner_l2_l3_len" field in the rte_mbuf structure.
The "packet_type" field is used to indicate ordinary packet format and also
tunneling packet format such as IP in IP, IP in GRE, MAC in GRE and MAC in UDP.
The "inner_l2_len" and the "inner_l3_len" fields are added
in the second cache line, they use 2 bytes for TX offloading of tunnels.

Signed-off-by: Jijiang Liu <jijiang.liu@intel.com>
Acked-by: Helin Zhang <helin.zhang@intel.com>
Tested-by: Yong Liu <yong.liu@intel.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>