nl80211: add 6GHz band definition to enum nl80211_band

nl80211: add 6GHz band definition to enum nl80211_band

In the 802.11ax specification a new band is introduced, which
is also proposed by FCC for unlicensed use. This band is referred
to as 6GHz spanning frequency range from 5925 to 7125 MHz.

Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Reviewed-by: Leon Zegers <leon.zegers@broadcom.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Link: https://lore.kernel.org/r/1564745465-21234-2-git-send-email-arend.vanspriel@broadcom.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>