RDMA/core: Calculate UDP source port based on flow label or lqpn/rqpn

Calculate and set UDP source port based on the flow label. If flow label
is not defined in GRH then calculate it based on lqpn/rqpn.

Link: https://lore.kernel.org/r/20220106180359.2915060-2-yanjun.zhu@linux.dev


Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>