xfs: fix errors in various verifiers

During a code audit of the effectiveness of the new online directory
repair code, it was discovered that XFS does not check the owner fields
of the dir3 free, data, and block format metadata blocks.  It was
further discovered that when the dir3 free block verifier rejects a
block, it does not leave the incore buffer in the correct state.
Correct these problems.

For v2, we actually stale the buffer so that it won't hang around on the
LRU, and fix a UAF bug I introduced into the attr inactivation bailout
code.