xfs: Hoist xfs_attr_node_addname

This patch hoists the later half of xfs_attr_node_addname into
the calling function.  We do this because it is this area that
will need the most state management, and we want to keep such
code in the same scope as much as possible

Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>