net: lockless SO_PASSCRED, SO_PASSPIDFD and SO_PASSSEC

sock->flags are atomic, no need to hold the socket lock
in sk_setsockopt() for SO_PASSCRED, SO_PASSPIDFD and SO_PASSSEC.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>