panic: tcp_do_segment: sent too much

Hi,

I seem to have hit this panic during normal laptop usage with a -CURRENT 
running at 2832af7b4ea256b18ef4dbf2ff97a50765f0609a:

panic: tcp_do_segment: sent too much
cpuid = 5
time = 1736731772
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 
0xfffffe015b74b9b0
vpanic() at vpanic+0x136/frame 0xfffffe015b74bae0
panic() at panic+0x43/frame 0xfffffe015b74bb40
tcp_do_segment() at tcp_do_segment+0x2998/frame 0xfffffe015b74bc20
tcp_input_with_port() at tcp_input_with_port+0x10f8/frame 0xfffffe015b74bd70
tcp_input() at tcp_input+0xb/frame 0xfffffe015b74bd80
ip_input() at ip_input+0x28f/frame 0xfffffe015b74bde0
swi_net() at swi_net+0x19b/frame 0xfffffe015b74be60
ithread_loop() at ithread_loop+0x266/frame 0xfffffe015b74bef0
fork_exit() at fork_exit+0x82/frame 0xfffffe015b74bf30
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe015b74bf30

Doing a little bit of inspection:

(kgdb) print tp->t_dupacks
$1 = 1
(kgdb) print tp->snd_limited
$6 = 0 '\000'
(kgdb) p/x tp->t_flags
$4 = 0x10000264
(kgdb) print maxseg
$1 = 1428

`sent` appears to be optimized out.  As far as I know, I don't hit this 
one often, but I'm wondering if there's anything else useful I could 
extract here / if anyone has a theory about what happened.

Thanks,

Kyle Evans