Under certain conditions on certain versions of Hyper-V, the RNDIS rxfilter is _not_ zero on the hypervisor side after the successful RNDIS initialization, which breaks the assumption of any following code (well, it breaks the RNDIS API contract actually). Clear the RNDIS rxfilter explicitly, drain packets sneaking through, and drain the interrupt taskqueues scheduled due to the stealth packets.

Reported-by: dexuan@