Add keyword to disable rig mode setting

[darvark]

Tested with FTdx3000, os: Elementary OS 7. Test case: Rig setup for bands: 40,20,15m to SSB, for 80m for CW. FOLLOW_MODE enabled in logcfg.dat, tlf started on 80m with CW mode. Switching band on tlf will cause to switch modulation on rig to CW. In case when FOLLOW_MODE is disabled, then changing bands will not cause switching mode on rig to CW, just new band which is visible in tlf.