We have fixed using channel number as internal parameter instead of
chan frequency with change I60fe37d7d716eeaceaa00f3fb59c77b629ebacac,
but variables name are still chan which might cause confused to reader.
Rename all places where "chan" to "chan_freq", which actually channel
frequency used. And alter miss APIs which still expect channel number.
Change-Id: I948cbad133a17093f49384b563966d2c53b51707
CRs-Fixed: 3033951