Revert "fs/9p: search open fids first"

Revert "fs/9p: search open fids first"

This reverts commit cae4be701ebd0e7e1b7cd8c18c7627df74875922.

That commit was meant as a fix for setattrs with by fd (e.g. ftruncate)
to use an open fid instead of the first fid it found on lookup.
The proper fix for that is to use the fid associated with the open file
struct, available in iattr->ia_file for such operations, and was
actually done just before in 7bccac4f976e ("9p: retrieve fid from file
when file instance exist.")
As such, this commit is no longer required.

Furthermore, changing lookup to return open fids first had unwanted side
effects, as it turns out the protocol forbids the use of open fids for
further walks (e.g. clone_fid) and we broke mounts for some servers
enforcing this rule.

Note this only reverts to the old working behaviour, but it's still
possible for lookup to return open fids if dentry->d_fsdata is not set,
so more work is needed to make sure we respect this rule in the future,
for example by adding a flag to the lookup functions to only match
certain fid open modes depending on caller requirements.

Link: https://lkml.kernel.org/r/20220130130651.712293-1-asmadeus@codewreck.org
Fixes: cae4be701ebd ("fs/9p: search open fids first")
Cc: stable@vger.kernel.org # v5.11+
Reported-by: ron minnich <rminnich@gmail.com>
Reported-by: ng@0x80.stream
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>