only pattern of esp-idf log lines are sent to syslog server

caused by those upstream issues:

• https://github.com/esp-rs/esp-idf-sys/issues/212
• https://github.com/esp-rs/rust/issues/177
• https://github.com/lights0123/printf-compat/issues/8
• https://users.rust-lang.org/t/esp-idf-logger-redirection-vprintf-variadic-function/95568/8