net/mlx5e: Consider internal buffers size in port buffer calculations

Currently, when a user triggers a change in port buffer headroom
(buffers 0-7), the driver checks that the requested headroom does
not exceed the total port buffer size. However, this check does not
take into account the internal buffers (buffers 8-9), which are also
part of the total port buffer. This can result in treating invalid port
buffer change requests as valid, causing unintended changes to the shared
buffer.

To address this, include the internal buffers size in the calculation of
available port buffer space which ensures that port buffer requests do not
exceed the correct limit.

Furthermore, remove internal buffers (8-9) size from the total_size
calculation as these buffers are reserved for internal use and are not
exposed to the user.

While at it, add verbosity to the debug prints in
mlx5e_port_query_buffer() function to ease future debugging.

Fixes: ecdf2dad ("net/mlx5e: Receive buffer support for DCBX")
Signed-off-by: Maher Sanalla <msanalla@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>