Do not rely linux kernel's headers - preparing for network tuners (SAT-IP)

This is a complete migration to use the own mux configuration scheme without
the system limitations to allow write backends for the network tuners like
SAT-IP servers.

Other comments:

I'd like to move the DVB Mux / Network configuration files from $CFG/input/linuxdvb/networks to $CFG/input/dvb/networks . The networks should be shared with all backends like LinuxDVB, SAT-IP and eventually IPTV (remote mux).

I purchased the GSS.BOX (a SAT-IP server with 4 tuners). I have the motivation to add the SAT-IP client code to tvheadend now.