[pvr.tvh] ignore mux packets when a channel switch is in progress
Revert "[pvr.tvh] a getDvrCutpoints response without a cutpoint list is not malformed,"

This reverts commit 063c21058ae175cd49c67620433778cb10fed8aa.
[pvr.tvh] remove unused m_started and m_startCond variables, relying on them
for the packet ignoring was obviously wrong
[pvr.tvh] reintroduce the "drop packets while switching channels" functionality