xfs: Hoist xfs_attr_leaf_addname

This patch hoists xfs_attr_leaf_addname into the calling function.  The
goal being to get all the code that will require state management into
the same scope. This isn't particularly aesthetic right away, but it is a
preliminary step to merging in the state machine code.

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