cfg80211: parse S1G Operation element for BSS channel

Extract the BSS primary channel from the S1G Operation
element.

Signed-off-by: Thomas Pedersen <thomas@adapt-ip.com>
Link: https://lore.kernel.org/r/20200922022818.15855-7-thomas@adapt-ip.com


[remove the goto bits]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>