"nm-glib-aux/nm-logging-fwd.h" provides macros like _LOGD() to be reused
by various parts which implement logging (by defining _NMLOG() accordingly).
libnm also has logging, however it uses different logging levels
aside LOGD_DEBUG.
Instead, implement _LOGD() using a define _LOGL_DEBUG, so that libnm can
redefine thos _LOGL_DEBUG defines and use the _LOGD() macro.
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