net/mlx5: Enable flow-steering for IB link

Get the relevant capabilities if supports ipoib_enhanced_offloads and
init the flow steering table accordingly.

Signed-off-by: Erez Shitrit <erezsh@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>