Fixes two bugs related to how sampling was triggered on the DCC signal: - between the time the nextSample_ counter underflowed and the timer underflowed, all interrupts were (incorrectly) triggering a sampling - the nextSample_ was underflowed twice, thus all edges after the underflow were triggering until we counted down 0x800000 counts from nextSample_
Fixes two bugs related to how sampling was triggered on the DCC signal:
- between the time the nextSample_ counter underflowed and the timer underflowed, all interrupts were (incorrectly) triggering a sampling
- the nextSample_ was underflowed twice, thus all edges after the underflow were triggering until we counted down 0x800000 counts from nextSample_

bakerstu/openmrn,bakerstu/openmrn,bakerstu/openmrn,bakerstu/openmrn,bakerstu/openmrn,bakerstu/openmrn