Bluetooth: controller: Fix DLE crossover assert

When initiating Data Length Change at the same instant the
crossover condition was not handled correctly causing the
controller to assert.

This fix will allow crossover of Data Length Update
procedure, and this collison is harmless as per Bluetooth
specification, and gracefully handled by the controller.

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