network,udev: refuse .link and .network settings with no matches

network,udev: refuse .link and .network settings with no matches

Two releases ago we started warning about this, and I think it is now to turn
this into a hard error. People get bitten by this every once in a while, and
there doesn't see to be any legitimate use case where the same .link or
.network files should be applied to _all_ interfaces, since in particular that
configuration would apply both to lo and any other interfaces. And if for
whatever reason that is actually desired, OriginalName=* or Name=* can be
easily added to silence the warning and achieve the effect.

(The case described in #12098 is particularly nasty: 'echo -n >foo.network'
creates a mask file, 'echo >foo.network' creates a "match all" file.)

Fixes #717, #12098 for realz now.