Split off __icmpv6_socket's sk->sk_dst_lock class, because it gets
used from softirqs, which is safe for __icmpv6_sockets (because they
never get directly used via userspace syscalls), but unsafe for normal
sockets.

Has no effect on non-lockdep kernels.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Acked-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>