Comment 4 for bug 1566468

That mlx4.conf file is also present in the same form on 14.04 cloudimg, which doesn't suffer from the issue. Or maybe the systemd module loader interprets this differently?

BTW the workaround I've found is to add the following to /etc/modprobe.d/blacklist.conf:

blacklist ib_iser
install ib_iser /bin/false