The filename seems to have changed to "iwlwifi-4965-1.ucode".
(As per diff:).
% cvs diff -r1.25 -r1.26 if_iwn.c
...
< if ((error = firmware_open("if_iwn","iwlwifi-4965.ucode", &fw)) != 0) {
---
> if ((error = firmware_open("if_iwn","iwlwifi-4965-1.ucode", &fw)) != 0)
Cheers, --Dave