Keep recordings when channel is deleted

When a channel is deleted, don't delete all existing recordings.
whitelist TBS 6981 card for SNR monitoring
timeshift: simplify total size locking
timeshift: increase timeshift play buffer period.
rawts: add missing (new) callback param to stop crash
dvb: stop psi_section_reassemble from skipping packets
dvr: stop possible NULL ptr if messing about with config
dvb: reworked dvb mux creation to only use NIT data
dvb: add some debug logging to dvb table code
dvb: allow off-air services to be inserted into the service list
Merge remote-tracking branch 'origin/pr/239'
Merge remote-tracking branch 'origin/pr/236'
Fix #1521 - dvr: some minor corrections to PR code

ensure that recordings are properly loaded in the event no channel
exists and that the internal channel name is preferred not the DE
on.
dvr: ensure subsystems are notified when dvr starts (and filename is set)
Fix #1569 - dvr: simplify filename cleanup