UPSTREAM: vsock: make listener child lock ordering explicit

UPSTREAM: vsock: make listener child lock ordering explicit

There are several places where the listener and pending or accept queue
child sockets are accessed at the same time.  Lockdep is unhappy that
two locks from the same class are held.

Tell lockdep that it is safe and document the lock ordering.

Originally Claudio Imbrenda <imbrenda@linux.vnet.ibm.com> sent a similar
patch asking whether this is safe.  I have audited the code and also
covered the vsock_pending_work() function.

Suggested-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 4192f672fae559f32d82de72a677701853cc98a7)
Bug: 121166534
Test: Ran cuttlefish with android-4.4 + VSOCKETS, VMWARE_VMCI_VSOCKETS
Signed-off-by: Cody Schuffelen <schuffelen@google.com>
Change-Id: I0cb7ee964057e9338971e1a2043ae17557feaec7