datapath: Fix table sparse annotations.

datapath: Fix table sparse annotations.

Several of the pointers in table.c were missing the correct
__rcu annotation and the pointer type in the actual declaration
of struct tbl was incorrect, so this fixes that.  It also adds
usage of rcu_dereference() to access an RCU protected pointer,
which is not strictly correct since an update side lock should
be held.  However, since the table is used in different pieces
of code and therefore different locks are used it is difficult
to know which lock to check without threading the information
though, which is ugly.  Since other places in table.c have this
same problem and this code should go away in the future it is
left as is.

Found with sparse.

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