app/testpmd: enable the heavyweight mode TCP/IPv4 GRO

app/testpmd: enable the heavyweight mode TCP/IPv4 GRO

The GRO library provides two modes to reassemble packets. Currently, the
csum forwarding engine has supported to use the lightweight mode to
reassemble TCP/IPv4 packets. This patch introduces the heavyweight mode
for TCP/IPv4 GRO in the csum forwarding engine.

With the command "set port <port_id> gro on|off", users can enable
TCP/IPv4 GRO for a given port. With the command "set gro flush <cycles>",
users can determine when the GROed TCP/IPv4 packets are flushed from
reassembly tables. With the command "show port <port_id> gro", users can
display GRO configuration.

The GRO library doesn't re-calculate checksums for merged packets. If
users want the merged packets to have correct IP and TCP checksums,
please select HW IP checksum calculation and HW TCP checksum calculation
for the port which the merged packets are transmitted to.

Signed-off-by: Jiayu Hu <jiayu.hu@intel.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>
Tested-by: Lei Yao <lei.a.yao@intel.com>