It is up to you to put "[architecture] what" into your commit message. Signed-off-by is a legal procedure, it should not be automated, you should do "git commit --signoff" yourself. "[PATCH]" is added by "git send-email".
If you don't want to setup your client properly and keep using some GUI or Web client, you can format your patch with "git format-patch" and submit whatever files it produces.
OpenWrt rightfully expects you to read at least "man giteveryday", which is titled "A useful minimum set of commands for Everyday Git" and includes "format-patch" and "send-email" in "INDIVIDUAL DEVELOPER (PARTICIPANT)" section.
If you don't want to setup your client properly and keep using some GUI or Web client, you can format your patch with "git format-patch" and submit whatever files it produces.
OpenWrt rightfully expects you to read at least "man giteveryday", which is titled "A useful minimum set of commands for Everyday Git" and includes "format-patch" and "send-email" in "INDIVIDUAL DEVELOPER (PARTICIPANT)" section.