mac80211: handle channel frequency offset

cfg80211_chan_def and ieee80211_channel recently gained a
frequency offset component. Handle this where it makes
sense (potentially required by S1G channels).

For IBSS, TDLS, CSA, and ROC we return -EOPNOTSUPP if a
channel with frequency offset is passed, since they may or
may not work. Once someone tests and verifies these
commands work on thos types of channels, we can remove
that error.

join_ocb and join_mesh look harmless because they use a
simple ieee80211_vif_use_channel(), which is using an
already verified channel, so we let those through.

Signed-off-by: Thomas Pedersen <thomas@adapt-ip.com>
Link: https://lore.kernel.org/r/20200402011810.22947-4-thomas@adapt-ip.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>