xfs: inactivate inodes any time we try to free speculative preallocations

Other parts of XFS have learned to call xfs_blockgc_free_{space,quota}
to try to free speculative preallocations when space is tight.  This
means that file writes, transaction reservation failures, quota limit
enforcement, and the EOFBLOCKS ioctl all call this function to free
space when things are tight.

Since inode inactivation is now a background task, this means that the
filesystem can be hanging on to unlinked but not yet freed space.  Add
this to the list of things that xfs_blockgc_free_* makes writer threads
scan for when they cannot reserve space.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>