net/mlx5: DR, Rework is_fw_table function

This patch handles the following two changes w.r.t. is_fw_table function:

1. When SW steering is asked to create/destroy FW table, we allow for
creation/destruction of only termination tables. Rename mlx5_dr_is_fw_table
both to comply with the static function naming and to reflect that we're
actually checking for FW termination table.

2. When the action 'go to flow table' is created, the destination flow
table can be any FW table, not only termination table. Adding function
to check if the dest table is FW table. This function will also be used
by the later creation of range match action, so putting it the header file.

Signed-off-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Reviewed-by: Alex Vesker <valex@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>