target_core_alua: Correct UA handling when switching states

When switching target port group ALUA states we need to send
one UA when setting the ALUA state to 'transitioning', and
another one once the final state has been set.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>