FROMGIT: selinux: vsock: Set SID for socket returned by accept()

For AF_VSOCK, accept() currently returns sockets that are unlabelled.
Other socket families derive the child's SID from the SID of the parent
and the SID of the incoming packet. This is typically done as the
connected socket is placed in the queue that accept() removes from.

Reuse the existing 'security_sk_clone' hook to copy the SID from the
parent (server) socket to the child. There is no packet SID in this
case.

Fixes: d021c344 ("VSOCK: Introduce VM Sockets")
Signed-off-by: David Brazdil <dbrazdil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 1f935e8e
 https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git master)
Link: https://lore.kernel.org/r/20210319130541.2188184-1-dbrazdil@google.com
Bug: 130668487
Change-Id: Idb656917cc600df7cb83cb15a6c0f0499045d77f