net/mlx5: Add missing inline to stub esw_add_restore_rule

When CONFIG_MLX5_ESWITCH is unset, clang warns:

In file included from drivers/net/ethernet/mellanox/mlx5/core/main.c:58:
drivers/net/ethernet/mellanox/mlx5/core/eswitch.h:670:1: warning: unused
function 'esw_add_restore_rule' [-Wunused-function]
esw_add_restore_rule(struct mlx5_eswitch *esw, u32 tag)
^
1 warning generated.

This stub function is missing inline; add it to suppress the warning.

Fixes: 11b717d6 ("net/mlx5: E-Switch, Get reg_c0 value on CQE")
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/ethernet/mellanox/mlx5/core/eswitch.h

@@ -677,7 +677,7 @@ static inline const u32 *mlx5_esw_query_functions(struct mlx5_core_dev *dev)
 
 static inline void mlx5_eswitch_update_num_of_vfs(struct mlx5_eswitch *esw, const int num_vfs) {}
 
-static struct mlx5_flow_handle *
+static inline struct mlx5_flow_handle *
 esw_add_restore_rule(struct mlx5_eswitch *esw, u32 tag)
 {
 	return ERR_PTR(-EOPNOTSUPP);