If the struct is used with a driver_udata it should have a trailing
driver_data flex array to mark it as having udata.

In most cases this forces the end of the struct to be aligned to u64 which
is needed to make the trailing driver_data naturally aligned.

Unfortunately We have a few cases where the base struct is not aligned to
8 bytes, these are marked with a u32 driver_data and userspace will check
for alignment issues when it compiles the driver.

Also remove the empty ib_uverbs_modify_qp_resp as nothing uses this.

pahole says there is no change to any struct sizes by this change.
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>