datapath: Don't check for RCU in free_buckets in table.

datapath: Don't check for RCU in free_buckets in table.

free_buckets() is only called in places where the lifetime of its
container has ended: on allocation failure and on deletion after
a grace period.  If the container can no longer be referenced then
neither can the buckets, so it is safe to directly free them.
sparse complains if the pointer is directly dereferenced and lockdep
complains if the RCU functions are used without some type of lock,
both of which are fine in this case.  This adds an explicit cast to
avoid the complaints.

Found with lockdep.

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