I posted this message on the gentoo forums : https://forums.gentoo.org/viewtopic-t-1004206.html but since I found this post (viewtopic.php?f=3&t=2180), I believe this forum may be better suited because the problem seems similar except I don't have the nvidia module.
To summarize my problem, I cannot load the bridge module; log says "vmap allocation for size 233472 failed: use vmalloc=<size> to increase size" but changing this value doesn't help. You may find some more context and logs extract/command output in the original post.
Since the first post, I managed to load the bridge module by unloading a module, trying to load bridge and reloading the first module; one module after another until success. But this is not really an acceptable solution.