Require the number of queues to be a power of 2.

[jhb]

Summary

Only use a power of 2 for the number of receive and transmit queues.
Using other values causes VMXNET3_CMD_ENABLE to fail. The Linux
driver also enforces this restriction.

Sponsored by: Norse

Test Plan

• Try to use multiq in a VM with 6 CPUs under ESX. With the default of 6 queues, the warning in dmesg triggered from CMD_ENABLE failing and no traffic was received. I then used the tunables to try other values and found that 2 and 4 worked but 3 did not.