Avoid dependencies but explicitly link the static library where it is
used.
This also fixes that we linked libnm-log-core into
libnm-settings-plugin-ifcfg-rh.so, which duplicated the symbols
while it should used them from NetworkManager.
"nm-compat.h" is not intended to be used by NetworkManager itself.
Instead, it's intended to be copied into the source tree of VPN plugins,
as adapter for different libnm versions.
Move it to "src/contrib/".
This file is not actually to be used by NetworkManager itself.
Instead, every (glib based) VPN plugin will want something like this,
hence we have a copy here.
Move it to a new directory "src/contrib/".
This helper code is already used by several of our unit tests.
Compile it as a separate library.
Previously, the source code lingered unmotivated under "shared/",
which is confusing.
