scan.cpp: perform T2 and T scan only, when frontend is actually supporting DVB-T2. This will also fix USB DVB-T full service scan and tunein issues with -1 entries in lamedb.

Signed-off-by: littlesat <littlesat99@yahoo.com>
Merge branch 'master' of git://git.code.sf.net/p/openpli/enigma2