Linux 3.10: Include linux/aio.h directly

This file needs bits from linux/aio.h, but gets them indirectly
from the inclusion of aio.h by sched.h.  That gets removed for
Linux 3.10.

Since this header is not of general interest elsewhere, just include
it directly here.

Reviewed-on: http://gerrit.openafs.org/9912
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit fca4252621b80c5126e1ae3d84a54da5ebc677ba)

Change-Id: I7da471ee033087592b9ec3f10331baf0135cc201
Reviewed-on: http://gerrit.openafs.org/9947
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>