IB/uverbs: UAPI pointers should use __aligned_u64 type

The ioctl() UAPIs are meant to be used by both user-space
and kernel ioctl() handlers.

Mostly, these UAPI structs tend to consist of simple types, but
sometimes user-space pointers may be passed between user-space and
kernel. We would like to avoid dereferencing a user-space pointer in
the kernel, thus - we always define RDMA_UAPI_PTR as a __aligned_u64
type.

Fixes: 1f7ff9d5

 ('IB/uverbs: Move to new headers and make naming consistent')
Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>