xfs: clean up xfs_inactive

The code to reserve log space and join the inode to the transaction is
common for all cases, so don't duplicate it.  Also remove the trivial
xfs_inactive_symlink_local helper which can simply be opencode now.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Rich Johnston <rjohnston@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>