net/tap: free mempool when closing

net/tap: free mempool when closing

When setup tx queues, we will create a mempool for the 'gso_ctx'.
The mempool is not freed when closing tap device. If free the tap
device and create it with different name, it will create a new
mempool. This maybe cause an OOM.

The snprintf function return value is not checked and the mempool
name may be truncated. This patch also fix it.

Fixes: 050316a88313 ("net/tap: support TSO (TCP Segment Offload)")
Cc: stable@dpdk.org
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>