IB: ucontext should be set properly for all cmd & ioctl paths

the Attempt to use the below commit to initialize the ucontext for the
uobject destroy path has shown that the below commit is incomplete.

Parts were reverted and the ucontext set up in the uverbs_attr_bundle was
moved to rdma_lookup_get_uobject which is called from the uobj_get_XXX
macros and rdma_alloc_begin_uobject which is called when uobject is
created.

Fixes: 3d9dfd06

 ("IB/uverbs: Add ib_ucontext to uverbs_attr_bundle sent from ioctl and cmd flows")
Signed-off-by: Shamir Rabinovitch <shamir.rabinovitch@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>