net: sched: sch_multiq: fix possible OOB write in multiq_tune()

In the Linux kernel, the following vulnerability has been resolved: net: sched: sch_multiq: fix possible OOB write in multiq_tune() q->bands will be assigned to qopt->bands to execute subsequent code logic after kmalloc. So the old q->bands should not be used in kmalloc. Otherwise, an out-of-bounds write will occur.