net/tap: support TSO (TCP Segment Offload)

net/tap: support TSO (TCP Segment Offload)

This commit implements TCP segmentation offload in TAP.
librte_gso library is used to segment large TCP payloads (e.g. packets
of 64K bytes size) into smaller MTU size buffers.
By supporting TSO offload capability in software a TAP device can be used
as a failsafe sub device and be paired with another PCI device which
supports TSO capability in HW.

For more details on librte_gso implementation please refer to dpdk
documentation.
The number of newly generated TCP TSO segments is limited to 64.

Reviewed-by: Raslan Darawsheh <rasland@mellanox.com>
Signed-off-by: Ophir Munk <ophirmu@mellanox.com>
Acked-by: Keith Wiles <keith.wiles@intel.com>