LSM: fix documentation for the socket_getpeersec_dgram hook

The socket_getpeersec_dgram hook was changed in the commit
"[AF_UNIX]: Kernel memory leak fix for af_unix datagram
getpeersec patch" (dc49c1f9). The arguments @secdata
and @seclen were changed to @sock and @secid. This patch
updates the documentation accordingly.
Signed-off-by: Denis Efremov <efremov@ispras.ru>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: James Morris <james.morris@microsoft.com>

include/linux/lsm_hooks.h

@@ -877,9 +877,9 @@
  *	the IP_PASSSEC option via getsockopt. It can then retrieve the
  *	security state returned by this hook for a packet via the SCM_SECURITY
  *	ancillary message type.
- *	@skb is the skbuff for the packet being queried
- *	@secdata is a pointer to a buffer in which to copy the security data
- *	@seclen is the maximum length for @secdata
+ *	@sock contains the peer socket. May be NULL.
+ *	@skb is the sk_buff for the packet being queried. May be NULL.
+ *	@secid pointer to store the secid of the packet.
  *	Return 0 on success, error on failure.
  * @sk_alloc_security:
  *	Allocate and attach a security structure to the sk->sk_security field,