MFC r322258, r324941, r324956, r325018

MFC r322258, r324941, r324956, r325018

r322258:
Make p1003_1b.aio_listio_max a tunable

p1003_1b.aio_listio_max is now a tunable. Its value is reflected in the
sysctl of the same name, and the sysconf(3) variable _SC_AIO_LISTIO_MAX.
Its value will be bounded from below by the compile-time constant
AIO_LISTIO_MAX and from above by the compile-time constant
MAX_AIO_QUEUE_PER_PROC and the tunable vfs.aio.max_aio_queue.

Reviewed by:	jhb, kib
Relnotes:	yes
Sponsored by:	Spectra Logic Corp
Differential Revision:	https://reviews.freebsd.org/D11601

r324941:
Remove artificial restriction on lio_listio's operation count

In r322258 I made p1003_1b.aio_listio_max a tunable. However, further
investigation shows that there was never any good reason for that limit to
exist in the first place. It's used in two completely different ways:

* To size a UMA zone, which globally limits the number of concurrent
  aio_suspend calls.

* To artifically limit the number of operations in a single lio_listio call.
  There doesn't seem to be any memory allocation associated with this limit.

This change does two things:

* Properly names aio_suspend's UMA zone, and sizes it based on a new constant.

* Eliminates the artifical restriction on lio_listio. Instead, lio_listio
  calls will now be limited by the more generous max_aio_queue_per_proc. The
  old p1003_1b.aio_listio_max is now an alias for
  vfs.aio.max_aio_queue_per_proc, so sysconf(3) will still work with
  _SC_AIO_LISTIO_MAX.

Reported by:	bde
Reviewed by:	jhb
Sponsored by:	Spectra Logic Corp
Differential Revision:	https://reviews.freebsd.org/D12120

r324956:
Bump man page revision dates for r324941

Reported by:	jhb
X-MFC-with:	324941
Sponsored by:	Spectra Logic Corp

r325018:
Fix aio_suspend in 32-bit emulation

An off-by-one error has been present since the system call was first present
in 185878.  It additionally became a memory corruption bug after change
324941.  The failure is actually revealed by our existing AIO tests.
However, apparently nobody's been running those in 32-bit emulation mode.

Reported by:	Coverity, cem
CID:		1382114
X-MFC-With:	324941
Sponsored by:	Spectra Logic Corp