mac80211: add freq_offset to RX status

RX status needs a KHz component, so add freq_offset. We
can reduce the bits for the frequency since 60 GHz isn't
supported.

Signed-off-by: Thomas Pedersen <thomas@adapt-ip.com>
Link: https://lore.kernel.org/r/20200402011810.22947-5-thomas@adapt-ip.com


[fix commit message]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>