datapath: Don't directly access RCU protected pointers.

datapath: Don't directly access RCU protected pointers.

If RTNL lock is used to protected updates to RCU data structures
then it isn't necessary to use rcu_dereference() to access them if
RTNL is held.  This adds rtnl_dereference() to access these pointers
which has several benefits: documents the locking expectations;
checks that RTNL actually is held when run with lockdep; makes
sparse not complain about directly accessing RCU pointers.

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