- Add missing `sys/ttydefaults.h` include to `config.c`
- Restrict usage of `error.h` to glibc and uclibc only
- Avoid including `linux/if_tun.h` on non-glibc/uclibc to prevent
musl kernel/libc header conflicts
Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>
