xfs: check v5 superblock features early

xfs: check v5 superblock features early

When working on a new features that reuses the existing pad in the
superblock, I noticed that mounting such a file system on an old kernel
logs a rather confusing warning:

    XFS (vdc): Metadir superblock padding fields must be zero.

This is because we only validate the various feature fields in v5
superblocks after the common superblock validation helper is called.

Fix this by calling the feature validation first.

Fixes: eca383fcd63b ("xfs: refactor superblock verifiers")
Cc: <stable@vger.kernel.org> # v4.19
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>