There is no reason for this lock to be reader/writer since
the reader only has lock held for a very brief period.
The overhead of read_lock is more expensive than spinlock.

Compile tested only, I am not a decnet user.
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>