target: Unify __core_scsi3_update_aptpl_buf and core_scsi3_update_aptpl_buf

The __ version is only ever called from the regular version, so just
inline it. It's not too much more complex to handle both spinlocks in the
same function.

Signed-off-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>