net/mlx5e: Geneve, Keep tunnel info as pointer to the original struct

In mlx5e encap entry structure, IP tunnel info data structure is copied
by value. This approach worked till now, but it breaks when there are
encapsulation options, such as in case of Geneve.

These options are stored in the structure that is allocated adjacent to
the IP tunnel info struct, and not pointed at by any field in that struct.
Therefore, when copying the struct by value, we loose the address of the
original struct and can't get to the encapsulation options.

Fix the problem by storing the pointer to the tunnel info data instead.

Reviewed-by: Oz Shlomo <ozsh@mellanox.com>
Signed-off-by: Yevgeny Kliteynik <kliteyn@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>