Merge branch 'af_unix_MSG_PEEK'

Aaron Conole says:

====================
af_unix: return data from multiple SKBs on recv() with MSG_PEEK flag

This patch set implements a bugfix for kernel.org bugzilla #12323, allowing
MSG_PEEK to return all queued data on the unix domain socket, not just the
data contained in a single SKB.

This is the v3 version of this patch, which includes a suggested modification
by Eric Dumazet to convert the unix_sk() conversion macro to a static inline
function. These patches are independent and can be applied separately.

This set was tested over a 24-hour period, utilizing a loop continually
executing the bugzilla issue attached python code. It was instrumented with
a pr_err_once() ([   13.798683] unix: went there at least one time).

v2->v3:
 - Added Eric Dumazet's suggestion for #define to static inline
 - Fixed an issue calling unix_state_lock() with an invalid argument

v3->v4:
 - Eliminated an XXX comment
 - Changed from goto unlock to explicit unix_state_unlock() and break
====================

Signed-off-by: David S. Miller <davem@davemloft.net>