afs: Return raw code from background daemons

Currently, a background daemon processing a 'store' request will
return any error code in the 'code' field in the brequest structure,
for processing by anyone that's waiting for the response. Since any
waiter will not have access to the treq for the request, they won't be
able to call afs_CheckCode on that return code, so the background
daemon calls afs_CheckCode before returning its error code.

Currently, afs_close uses the 'code' value from the background daemon
as if it were not passed through afs_CheckCode. That is, if all
background daemons are busy, we get our 'code' directly from
afs_StoreOnLastReference, and if we use a background daemon, our
'code' is tb->code. But these values are two different things: the
return value from afs_StoreOnLastReference is a raw error code, and
the code from the background daemon (tb->code) has been translated
through afs_CheckCode.

This can be confusing, in particular for the scenario where a
StoreData fails because of network errors or because of a VBUSY error.
If we get a network error when the request went through a background
daemon, afs_CheckCode will translate this to ETIMEDOUT, which is
commonly value 110, the same as VBUSY. So, an ETIMEDOUT error from the
background daemon is difficult to distinguish from a VBUSY error from
a direct afs_StoreOnLastReference call. Either case can result in a
message to the kernel like the following:

  afs: failed to store file (110)

To resolve this, have the background daemon store both the 'raw' error
code, and the error code that has been translated through
afs_CheckCode. afs_close can then use the raw error code when
reporting messages like normal, but can still use the translated error
code to return to the caller, if it has a translated error. With this
change, now afs_close will always log "network problems" for a network
error, regardless of if the error came in via a background daemon or a
direct afs_StoreOnLastReference call.

In Irix's afs_delmap, we just remove the old usage of tb->code, since
the result was not used for anything.

Change-Id: I3e2bf7e36c1f098df16a1fdb0dc88b45ea87dfa9
Reviewed-on: http://gerrit.openafs.org/10633
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>