[OpenAFS] Documentation for `afsd` argument `files_per_subdir` is wrong (out of sync with the implementation)

[Ciprian Dorin Craciun]

Hello all!

I'm using OpenAFS on OpenSUSE, version 1.8.x (in fact 1.8.0 and 1.8.2
on two nodes), and although the documentation for the `afsd` daemon
states for `files_per_subdir` that:
~~~~
files_per_subdir -- Limits the number of cache files in each
subdirectory of the cache directory. The value of the option should be
the base-two log of the number of cache files per cache subdirectory
(so 10 for 1024 files, 14 for 16384 files, and so forth).
~~~~

It is in fact use without the exponential transformation.  I.e.
setting `-files_per_subdir 10` will actually result in exactly 10
files per directory, meanwhile `-files_per_subdir 1024` would
correctly result in 1K files.

Thanks,
Ciprian.