re: 10.99.9 amd64 panic

[matthew green <mrg%eterna.com.au@localhost>]

i just commited what i believe is a fix for this problem, and for
another potential memory leak i saw from inspection.

seems to work for me on an amd64 host, been through several down/up
sequences, though i did not force the memory alloc failure directly.

(annoyingly, it takes 10-11s to regain link to my switch when doing
this down/up sequence.)

i'll prepare a pullup for netbsd-10, too.


.mrg.