`conf-file conf.d/*` as default

[enihcam]

需求应用场景 请描述需求应用的场景和方式。

建议的方案 实现上述场景建议的方案。

to avoid adding conf-file conf.d/* to smartdns.conf everytime it is upgraded + overwritten

设备信息

1. 设备信息（CPU，厂家）

2. 固件信息

[pymumu]

Currently there is no conf.d directory, this directory only exists in openwrt version It needs to be discussed whether it is necessary to include this configuration item by default.

[enihcam]

Currently there is no conf.d directory, this directory only exists in openwrt version It needs to be discussed whether it is necessary to include this configuration item by default.

whenever smartdns is upgraded, a 3-way comparison over smartdns.conf (remote/local/modified) takes place and requires manual effort just because the modified version is one with only conf-file conf.d/* added.

adding /etc/smartdns/conf.d/ directory and conf-file conf.d/* will eliminate the manual effort.