Wake up the hardware before doing anything in sysctl.

This stops the panics that occur on MIPS platforms when doing say,
'sysctl dev.ath.0' whilst the MAC is asleep. The MIPS platform is
rather unforgiving in getting power-save register access wrong and you
will get all kinds of odd failures if you don't have things woken
up at the right times.

Tested:

• QCA9558 (TP-Link Archer C7 v2)
• AR9331 (Carambola 2)

.. with no VAPs configured and ath0 down (thus the MAC is definitely

asleep.)

PR: kern/201117