xfs: Hoist node transaction handling

This patch basically hoists the node transaction handling around the
leaf code we just hoisted.  This will helps setup this area for the
state machine since the goto is easily replaced with a state since it
ends with a transaction roll.

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>