idnode: allow NOSAVE options to be "loaded".

This is needed since this routine is used to also load config on creation.
So if a NOSAVE option is included there it will not load it. If it really
is NOSAVE it shouldn't be in the config files anyway (due to NOSAVE check
on actual save).
linuxdvb: added pre-defined mux configuration file support

This had been left out for too long and makes it awkward for novices
to setup the networks. The config is possibly not as nice as before where
it was presented as a tree. But this can be improved later.