GCC warns when the function definition and prototype do not agree on array bounds. Here the function prototype in vport.h is:

int mlx5_modify_nic_vport_mac_address(struct mlx5_core_dev *dev,
				      u16 vport, u8 mac[ETH_ALEN]);

Now, it may be that the prototype should be fixed instead because in the surrounding context, the other functions use pointers:

int mlx5_query_nic_vport_mac_address(struct mlx5_core_dev *mdev,
				     u16 vport, u8 *addr);
int mlx5_modify_nic_vport_mac_address(struct mlx5_core_dev *dev,
				      u16 vport, u8 mac[ETH_ALEN]);
int mlx5_set_nic_vport_current_mac(struct mlx5_core_dev *mdev, int vport,
				   bool other_vport, u8 *addr);

I think the reason the compiler cares is that the compiler can make optimization assumptions based on explicit array bounds. I think that the danger there is more the opposite case though where the function has a fixed bound and the prototype is missing the bounds, but GCC warns about any mismatch. It's easier to just fix these nits than to shut up the warning IMO.

But I will probably wait to see what Hans thinks though as in this case it's probably more consistent to patch the prototype in vport.h to use a pointer I think,