Use frequency instead of chan num for processing TDLS offchannel
req for preferred offchannel.
Since, after introduction of TDLS on 6 GHz band it is better to
process offchannel in frequency instead of channel numbers as
some of the channel numbers are repeated for 6 GHz.
Change-Id: Icd7084b9f3c407ad0ad104b7f0d2230e31e0b10d
CRs-Fixed: 3234920