NetBSD/amd64-current crashes during shutdown

[Tom Ivar Helbekkmo <tih%hamartun.priv.no@localhost>]

After upgrading to an August 29th snapshot of 7.99.1, my amd64 system
crashes during shutdown, always on the same assertion:

barsoom# crash -M netbsd.24.core -N netbsd.24
Crash version 7.99.1, image version 7.99.1.
System panicked: kernel diagnostic assertion "mutex_owned(softnet_lock)"
failed: file "/usr/src/sys/netinet/igmp.c", line 636 
Backtrace from time of crash is available.
crash> bt
_KERNEL_OPT_NARCNET() at 0
?() at ffff80001bfd7068
vpanic() at vpanic+0x145
kern_assert() at kern_assert+0x4f
igmp_sendpkt.isra.1() at igmp_sendpkt.isra.1+0x191
in_delmulti() at in_delmulti+0x3c
ip_freemoptions() at ip_freemoptions+0x25
in_pcbdetach() at in_pcbdetach+0xb9
udp_detach_wrapper() at udp_detach_wrapper+0x2f
soclose() at soclose+0x63
soo_close() at soo_close+0x16
closef() at closef+0x54
fd_close() at fd_close+0x19f
sys_close() at sys_close+0x20
syscall() at syscall+0x9a
--- syscall (number 6) ---
7f7ff703c3aa:

-tih
-- 
It doesn't matter how beautiful your theory is, it doesn't matter how smart
you are. If it doesn't agree with experiment, it's wrong.  -Richard Feynman