net/mlx5e: Check if inner FT is supported outside of create/destroy functions
Move the mlx5e_tunnel_inner_ft_supported() check for inner flow tables
support outside of mlx5e_create_inner_ttc_table() and
mlx5e_destroy_inner_ttc_table(). It allows to avoid accessing invalid
TIRNs of inner indirect TIRs. In a later commit these accesses will be
replaced by getters that will WARN if inner indirect TIRs don't exist.