xfs: clear incore AGFL_RESET state if it's not needed

Prior to commit 7ac2ff8b, when we loaded the incore perag structure
with information from the AGF header, we would set or clear the
pagf_agfl_reset field based on whether or not the AGFL list was
misaligned within the block.  IOWs, it's an incore state bit that's
supposed to cache something in the ondisk metadata.  Therefore, the code
still needs to support clearing the incore bit if (somehow) the AGFL
were to correct itself.

It turns out that xfs_repair does exactly this -- phase 4 loads the AGF
to scan the rmapbt for corrupt records, which can set NEEDS_AGFL_RESET.
The scan unsets AGF_INIT but doesn't unset NEEDS_AGFL_RESET.  Phase 5
totally rewrites the AGFL and fixes the alignment problem, didn't clear
NEEDS_AGFL_RESET historically, and reloads the perag state to fix the
freelist.  This results in the AGFL being reset based on stale data,
which then causes the new AGFL blocks to be leaked.  A subsequent
xfs_repair -n then complains about the leaks.

One could argue that phase 5 ought to clear this bit directly when it
reloads the perag AGF data after rewriting the AGFL, but libxfs used to
handle this for us, so it should go back to doing that.

Found by fuzzing flfirst = ones in xfs/352.

Fixes: 7ac2ff8b ("xfs: perags need atomic operational state")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/libxfs/xfs_alloc.c

@@ -3045,6 +3045,8 @@ xfs_alloc_read_agf(
 		pag->pagf_refcount_level = be32_to_cpu(agf->agf_refcount_level);
 		if (xfs_agfl_needs_reset(pag->pag_mount, agf))
 			set_bit(XFS_AGSTATE_AGFL_NEEDS_RESET, &pag->pag_opstate);
+		else
+			clear_bit(XFS_AGSTATE_AGFL_NEEDS_RESET, &pag->pag_opstate);
 
 		/*
 		 * Update the in-core allocbt counter. Filter out the rmapbt