net/mlx5: Remove encap entry pointer from the eswitch flow attributes

Encap wise, the tc eswitch flow attribute struct needs to have
only the encap ID which is programmed later to the HW and none
of the higher level encap params, fix that.

This patch doesn't change any functionality.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>