husb: Make control transactions asynchronous (Max Krasnyansky)

husb: Make control transactions asynchronous (Max Krasnyansky)

USB is 99.8% async now :). 0.2% is the three control requests that
we need to execute synchronously. We could off-load that to a thread
or something but it's not worth the pain since those requests are
performed only during device initialization (ie when device is
connected to the VM).

The change is a bit bigger than I wanted due to the fact that generic
handle_packet()/handle_control() interface was not designed for
async transactions. So I ended up adding custom handle_packet()
code to usb-linux. We can make that generic if/when some other
component needs it.

Signed-off-by: Max Krasnyansky <maxk@kernel.org>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5204 c046a42c-6fe2-441c-8c8c-71466251a162