I want to set /sys/class/net/wwan0/qmi/raw_ip, and I don't want to do it by writing a shell script to take wwan0 down set it, then put wwan0 back up as a systemd unit. I'm trying this on Raspbian Stretch, but I doubt the distribution matters much for this.
I tried a bunch of ways of expressing this as a kernel cmdline argument, with no luck (net.qmi.raw_ip=Y, net.qmi_wwan.raw_ip=Y, qmi_wwan.raw_ip=Y, etc).
I tried adding net.wwan0.qmi.raw_ip=1 to /etc/sysctl.conf. That produced this error: [ 23.918756] qmi_wwan 1-1.5:1.3 wwan0: Cannot change a running device
Which means that it didn't do it until wwan0 was already up.
I tried adding denyinterfaces wwan0 to /etc/dhcpcd.conf, but same result.