repair: protect inode chunk tree records with a mutex

repair: protect inode chunk tree records with a mutex

Phase 6 accesses inode chunk records mostly in an isolated manner.
However, when it finds a corruption in a directory or there are
multiple hardlinks to an inode, there can be concurrent access
to the inode chunk record to update state.

Hence the inode record itself needs a mutex. This protects all state
changes within the inode chunk record, as well as inode link counts
and chunk references. That allows us to process multiple chunks at
once, providing concurrency within an AG as well as across AGs.

The inode chunk tree itself is not modified in the directory
scanning and rebuilding part of phase 6 which we are making
concurrent, hence we do not need to worry about locking for AVL tree
lookups to find the inode chunk records themselves. Therefore
internal locking is all we need here.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>