Bridge can be managed by "ip" from iproute2. And even this is single (known to me) way to set bridge MTU (only on "ip link create"). My patch conservative keep brctl where possible (if present and no MTU). Reproducible: Always
Created attachment 440668 [details, diff] netifrc: iproute2 & MTU for bridges
Please don't patch the last stable version, but rather look at what's already in Git. Wherein you'll see that iproute2 has been supported for more than 6 months. Your mtu change should also not be needed, as the regular mtu handling of iproute2 should be sufficient.
0.4.0 is out now, test that, the base MTU functionality should just work.
No. "Base MTU functionality" not working in current kernels (now - 4.6.3). Can look Google about people question too. It work only on interface creation (not change) - "ip link add". But in 0.4.0 patch more simple (and now respect config_vars).
Created attachment 440760 [details, diff] netifrc-0.4.0: iproute2 & MTU for bridges
PS Just try to create bridge and change mtu to jumbo 9000. And then try to create with mtu 9000 from scratch.
Created attachment 440764 [details, diff] netifrc-0.4.0: iproute2 & MTU for bridges fixed just add "mtu" to "local"
PPS Comment ("iproute2") just dummy copied, sorry.
Created attachment 440766 [details, diff] netifrc-0.4.0: MTU for bridges omg sorry, src/dst patch path... many jobs, many mistakes...
shit. fix path, yourself you are not dummy...
good: https://raw.githubusercontent.com/mahatma-kaganovich/raw/master/app-portage/ppatch/files/extensions/net-misc/netifrc/prepare/netifrc-bridge-iproute2-4-2.patch