net/mlx5: Remove unnecessary checks for slow path flag

After previous changes, caller (mlx5e_tc_offload_fdb_rules()) already
checks for the slow path flag, and if set won't call offload/unoffload
sample.

Signed-off-by: Paul Blakey <paulb@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>