Avoid sleeping with mutex held in kern_ndis.c.

Avoid sleeping with mutex held in kern_ndis.c.

Remove unused fields from ndis_miniport_block.

Fix a bug in KeFlushQueuedDpcs() (we weren't calculating the kq pointer
correctly).

In if_ndis.c, clear the IFF_RUNNING flag before calling ndis_halt_nic().

Add some guards in kern_ndis.c to avoid letting anyone invoke ndis_get_info()
or ndis_set_info() if the NIC isn't fully initialized. Apparently, mdnsd
will sometimes try to invoke the ndis_ioctl() routine at exactly the
wrong moment (to futz with its multicast filters) when the interface
comes up, and can trigger a crash unless we guard against it.