vol: consolide afs_xxxx macros in ihandle.h

vol: consolide afs_xxxx macros in ihandle.h

Various definitions of afs_open, afs_stat, etc. were
scattered across the .c sources within the vol package.
Consolidate them all in ihandle.h which is included in
all of the files and contains the OS_xxxx macros which
will substitute for many afs_xxxx calls in future patchsets.

Change-Id: I72363332fd5f1d330e225df51c68d4c113b59f3b
Reviewed-on: http://gerrit.openafs.org/4147
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>