MFC r267240:
Resolve a deadlock setting the USB configuration index from userspace
on USB HUBs by moving the code into the USB explore threads. The
deadlock happens because child devices of the USB HUB don't have the
expected reference count when called from outside the explore
thread. Only the HUB device itself, which the IOCTL interface locks,
gets the correct reference count.

MFC r260588 and r260589:
- Separate I/O errors from reception of STALL PID.
- Implement better error recovery for Transaction Translators, TTs,
found in High Speed USB HUBs which translate from High Speed USB into
FULL or LOW speed USB. In some rare cases SPLIT transactions might get
lost, which might leave the TT in an unknown state. Whenever we detect
such an error try to issue either a clear TT buffer request, or if
that is not possible reset the whole TT.

MFC r267240:
Resolve a deadlock setting the USB configuration index from userspace
on USB HUBs by moving the code into the USB explore threads. The
deadlock happens because child devices of the USB HUB don't have the
expected reference count when called from outside the explore
thread. Only the HUB device itself, which the IOCTL interface locks,
gets the correct reference count.

MFC r260588 and r260589:
- Separate I/O errors from reception of STALL PID.
- Implement better error recovery for Transaction Translators, TTs,
found in High Speed USB HUBs which translate from High Speed USB into
FULL or LOW speed USB. In some rare cases SPLIT transactions might get
lost, which might leave the TT in an unknown state. Whenever we detect
such an error try to issue either a clear TT buffer request, or if
that is not possible reset the whole TT.