RDMA/mlx5: Consider eswitch encap mode

When flow steering is created, then the encap support should
consider the eswitch encap mode. If the eswitch flow table (FDB)
supports encap then it shouldn't be supported on NIC RX flow tables.

Fixes: 4adda112

 ('RDMA/mlx5: Enable decap and packet reformat on flow tables')
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>