Linux: cache bypass: deal with the afs_serverHasNo64Bit case

Linux: cache bypass: deal with the afs_serverHasNo64Bit case

Deal correctly with the case of a server with no 64-bit fetch
support.  In that case, the code needs to fallback to the standard
FetchData call, similar to what happens in afs_fetchstore.c.
Move existing check out of 64-bit-only branch so servers
already known to be non-64-bit and not merely those newly
discovered so execute the non-64-bit FetchData.

Change-Id: I505ce6d88072bc3ee5208863717395a78f8562fa
Reviewed-on: http://gerrit.openafs.org/2319
Reviewed-by: Matt Benjamin <matt@linuxbox.com>
Tested-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>