net/mlx5e: Remove exposure of IPsec RX flow steering struct

After previous commit, which unified various IPsec creation modes,
there is no need to have struct mlx5e_ipsec_rx exposed in global
IPsec header. Move it to ipsec_fs.c to be placed together with
already existing struct mlx5e_ipsec_tx.

Fixes: 1762f132 ("net/mlx5e: Support IPsec packet offload for RX in switchdev mode")
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>