net: decnet: Fix sleeping inside in af_decnet

The release_sock() is blocking function, it would change the state
after sleeping. use wait_woken() instead.

Fixes: 1da177e4

 ("Linux-2.6.12-rc2")
Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
Signed-off-by: David S. Miller <davem@davemloft.net>