IB/mlx5: LAG QP load balancing

When LAG is active, QP tx affinity (the physical port
to which a QP is affined, or the TIS in case of raw-eth)
is set in a round robin fashion during state transition
from RESET to INIT.

Signed-off-by: Aviv Heller <avivh@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>