datapath: Don't rcu_dereference() objects in table.

Each time that we modify the flow/port table, we reallocate the
array of pointers to objects in a particular bucket.  We then use
RCU to update the link to that bucket.  This means that we don't
need to use RCU to access the individual object pointers, since
they are constant for a given instance of the bucket data structure.
This doesn't cause a problem per se (though it does restrict the
optimizations that the compiler can perform and adds a memory barrier
on Alpha).  However, it is confusing and inconsistent since the
pointers are not protected by RCU and we don't use rcu_assign_pointer().

Found by sparse.

Signed-off-by: Jesse Gross <jesse@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>