port-amd64/41174: uhmodem(4) hotplug chashes on amd64

[evaldo%gardenali.biz@localhost]

>Number:         41174
>Category:       port-amd64
>Synopsis:       uhmodem(4) hotplug chashes on amd64
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-amd64-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Apr 09 03:45:00 +0000 2009
>Originator:     Evaldo Gardenali
>Release:        5.99.10 checked out 20090408 evening UTC
>Organization:
>Environment:
>Description:
Crash occurs when plugging a Huawei e156 modem after the system has booted. 
Huawei e156 presents two virtual serial ports (first for connection, second for 
management/status), one virtual CD drive with windows drivers, one microSD slot.

http://evaldo.gardenali.biz/NetBSD-5.99.10-amd64/DSCN1722.JPG
http://evaldo.gardenali.biz/NetBSD-5.99.10-amd64/DSCN1724.JPG

Problem does not happen when plugging the modem with machine powered off and 
then booting into NetBSD. PPP Session is established, bandwidth and latency are 
reasonable, connection is stable (did a whole cvs-over-ssh fetch for src/)

Therefore, this PR validates port-amd64/40991, it should be implemented for 
better port-amd64 experience.

Problem does not happen on 5.99.10 ***i386**** 200904070000Z, using same 
laptop, same usb port.

>How-To-Repeat:
Compile a GENERIC kernel, adding only the following lines: (copied from PR# 
port-amd64/40991)

# Huawei E220 3G/HSDPA modem
uhmodem* at uhub? port ? configuration ? interface ?
ucom*   at uhmodem? portno ?

Boot system with usb modem unplugged
Plug it (both with a microSD card or without a microSD card produce the same 
results)
Wait until NetBSD detaches the device and reattaches it
CRASH!


>Fix: