net/mlx5e: E-Switch, Check device is PF when stopping esw offloads

Checking sriov is done on the pci device so it can return true
on other devices like SF but nothing should be done in this case.
Add a check that the device is PF.

Signed-off-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>