net/mlx5: E-Switch, Fix default encap mode

Encap mode is related to switchdev mode only. Move the init of
the encap mode to eswitch_offloads. Before this change, we reported
that eswitch supports encap, even tough the device was in non
SRIOV mode.

Fixes: 7768d197 ('net/mlx5: E-Switch, Add control for encapsulation')
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>