net/mlx5_core: Add transport domain alloc/dealloc support

Each transport object, namely TIR and TIS, must have a transport domain
number (TDN) identifier.

The driver wrongly assumed that it is OK to use TDN=0 without explicit
TDN allocation from the device.

The TDN will also be used for isolating different processes once user
mode Ethernet will be supported.

Signed-off-by: Achiad Shochat <achiad@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>