net/wifibox-core: fix build

Apparently there is a bug in the upstream Makefile and the
devd configuration file is always created in the staging
directory, but because the @comment prefix is used for FreeBSD
14 and later, it is ignored and excluded from the package.

Obtained from: https://github.com/pgj/freebsd-wifibox-port/commit/0534401cfc9f4722a7d9c93ade5695916ad3d598