Bluetooth: controller: Fix regression in ctrl tx queue handling

Fix control Tx buffer leak into data Tx pool that happens
after a cross-over control procedure response was paused due
to currently active encryption setup procedure, and a new
control Tx PDU in addition to the paused one is enqueued
thereafter.

When the control tx PDUs is resumed but not yet enqueued
towards the radio, if there is a new control Tx PDU enqueued
then the paused control Tx PDU is not set as the head of the
control PDUs in the Tx queue. This caused the paused control
Tx PDU to be associated with data Tx pool, hence causing the
incorrect release into data Tx pool.

Relates to the commit bff76b4c ("Bluetooth: controller:
split: Fix control tx queue handling") and to the
commit 6991d099 ("Bluetooth: controller: Fix control tx
queue handling").

Fixes #32898.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>