rdma: Move RDMA UAPI header file to be under RDMA responsibility

rdma: Move RDMA UAPI header file to be under RDMA responsibility

In iproute2 package, the updates of UAPIs files are performed
after the needed feature lands in kernel's net-next tree.

Such development flow created delays to the rdma tool developers,
who uses rdma-next tree as a basis for their work.

Move RDMA UAPI file to be under rdma/ folder, so whole responsibility
of syncing this file will be on them.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: David Ahern <dsahern@gmail.com>