app/testpmd: fix tunnel offload validation

app/testpmd: fix tunnel offload validation

Tunnel offload API allows application to restore packet to
its original form if chain of flows missed after DECAP action.
The main idea of the tunnel offload API was to query port PMD
to provide flow elements - actions or items.
Flow elements supplied by PMD are merged with original flow rule
elements provided by testpmd operator to create a new flow rule,
optimal for PMD, to implement the tunnel offload API.
That flow rule transformation is hidden form testpmd operator and uses
internal testpmd resources.

Current testpmd did not release tunnel offload resources if flow rule
validation failed.

The patch always releases tunnel offload resources after flow rule
validation returns.

Fixes: 1b9f274623b8 ("app/testpmd: add commands for tunnel offload")
Cc: stable@dpdk.org
Signed-off-by: Gregory Etelson <getelson@nvidia.com>
Reviewed-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
Acked-by: Aman Singh <aman.deep.singh@intel.com>