datapath: Add casts for direct freeing of RCU data.

datapath: Add casts for direct freeing of RCU data.

There are a few places where we have two levels of RCU protected
data to allow the second level to change independently of the
first.  Although the two pieces are independent, they have the
same users and lifetime of the first level always exceeds that
of the second level.  This means that we can directly free the
second level when it is safe to free the first.  This implies
that we directly access RCU-protected data, which is generally
not allowed.  There are no locks to check, so none of the normal
RCU functions apply.  Instead, this adds an explicit cast.

Found with sparse.

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