Make p1003_1b.aio_listio_max a tunable

[asomers]

Summary

Make 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.

Test Plan

sys/aio/lio_kqueue_test with different values for IOCBS_PER_LIO and
p1003_1b.aio_listio_max

[jhb]

sys/kern/posix4_mib.c

76

Even though this is not enabled, probably best to still add the macro here as well. Eventually we should probably just remove the disabled code.

sys/kern/vfs_aio.c

398

Blank line before comment (bde@ would probably say the comment is banal and can just be removed)

418–419

Add missing spaces around '*' while here.

1956

I'd rather make aio_listio_max a static global variable in vfs_aio.c and not call p31b_getcfg() in all these places.

2161

Extra blank line?

[asomers]

Store aio_listio_max as a static variable in vfs_aio.c instead of in
posix4_mib.c's facility array.

[jhb]

sys/kern/vfs_aio.c

172

Hmm, I think I do like this approach and would be a fan of moving all the AIO-related MIBs into this file. However, I think it would be useful to check in with kib@ and possibly bde@ before moving away from p1b_*().

[kib]

I am fine with the move of all aio-related sysctls.