ATSC DVB tuner fails to initialize

[jpoet]

As of [d81335eec] mythbackend fails to initialize ATSC DVB tuner with ID:

LGDT3306A VSB/QAM Frontend

When starting mythbackend With [4a2be05d2] I see:

2019-03-24 18:07:07.939094 I [19814/19814] CoreContext recorders/dvbchannel.cpp:446 (CheckOptions) - DVBChan[1](/dev/dvb/adapter0/frontend0): 545000000 8vsb a auto auto a a auto a v fec: auto msys: UNDEFINED rolloff: 0.35
2019-03-24 18:07:07.939267 I [19814/19814] CoreContext recorders/dvbchannel.cpp:742 (Tune) - DVBChan[1](/dev/dvb/adapter0/frontend0): 
Old Params: 0 auto a auto auto a a auto a v fec: auto msys: UNDEFINED rolloff: 0.35
New Params: 545000000 8vsb a auto auto a a auto a v fec: auto msys: UNDEFINED rolloff: 0.35
2019-03-24 18:07:07.939273 I [19814/19814] CoreContext recorders/dvbchannel.cpp:754 (Tune) - DVBChan[1](/dev/dvb/adapter0/frontend0): Tune(): Tuning to 545000000Hz
2019-03-24 18:07:08.541472 I [19814/19814] CoreContext recorders/dvbchannel.cpp:1526 (wait_for_backend) - DVBChan: wait_for_backend: Status: Signal,Carrier,FEC Stable,Sync,Lock,
2019-03-24 18:07:08.541481 I [19814/19814] CoreContext recorders/dvbchannel.cpp:896 (Tune) - DVBChan[1](/dev/dvb/adapter0/frontend0): Tune(): Frequency tuning successful.

With [d81335ee] I get:

2019-03-24 18:06:55.109481 E [16172/16172] CoreContext dtvmultiplex.cpp:352 (ParseTuningParams) - DTVMux: ParseTuningParams -- Unknown tuner type = 0xffffffff80000000
2019-03-24 18:06:55.109493 E [16172/16172] CoreContext recorders/dtvchannel.cpp:281 (SetChannelByString) - DTVChan[1](/dev/dvb/adapter0/frontend0): SetChannelByString(2_1): Failed to initialize multiplex options
2019-03-24 18:06:55.109496 I [16172/16172] CoreContext recorders/dtvchannel.cpp:311 (SetChannelByString) - DTVChan[1](/dev/dvb/adapter0/frontend0): SetChannelByString(2_1): failure

Let me know if you need more information.

[Klaas de Waal <kdewaal@…>]

In 93b6c5ab8/mythtv:

DVB tuner delivery system read from device

The delivery system, which is used to determine
the tuner type, is now read back from the tuner after the
tuner has been configured with the value in the database
table capturecard/inputname.

If the database does not have a valid value then
the tuner is not configured and the tuner type is
determined from the delivery system that is currently
configured in the tuner, either by power-on default
or by the dvb-fe-tool.

Previously, only the delivery system value from the
database was used to determine the tuner type.
This failed if there was no delivery system
configured in the database for that tuner.

Fixes #13434