Currently wlan_hdd_mgmt_tx path is still using legacy API to convert
channel frequency to number, it is not applicable for 6Ghz channel if
convert it back from number to frequency.
Fix it by replace all places where using legacy API to convert channel
and use channel frequency from supplicant directly. It can fix mgmt tx
from supplicant on 6Ghz channel.
Change-Id: I60fe37d7d716eeaceaa00f3fb59c77b629ebacac
CRs-Fixed: 3024898