net/mlx5: fix tunnel offload freeing

net/mlx5: fix tunnel offload freeing

PMD did not remove tunnel offload object from tunnels database before
it released the object memory. As the result, the tunnels database
become corrupted and subsequent search operations triggered PMD crash.
The patch removes tunnel offload object from the tunnels database when
the object is not in-use by PMD any more.

Fixes: bc1d90a3cf6f ("net/mlx5: fix build with Direct Verbs disabled")

Signed-off-by: Gregory Etelson <getelson@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>