net/mlx5: E-switch, Combine metadata enable/disable functionality

Except bit toggling code, rest of the code is same to enable/disable
metadata passing functionality.
Hence, combine them to single function and control using enable flag.

Also instead of checking metadata supported at multiple places,
fold into the helper function.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>