IB/uverbs: Add ioctl support for 32bit processes

32 bit processes running on a 64 bit kernel call compat_ioctl so that
implementations can revise any structure layout issues. Point compat_ioctl
at our normal ioctl because:

- All our structures are designed to be the same on 32 and 64 bit, ie we
  use __aligned_u64 when required and are careful to manage padding.

- Any pointers are stored in u64's and userspace is expected
  to prepare them properly.

Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>