mac80211: radiotap: Use BIT() instead of shifts

IEEE80211_RADIOTAP_EXT has a value of 31, which means if shift was ever
cast to 64-bit, the result would become sign-extended. As a matter of
robustness, just replace all the open-coded shifts with BIT().

Suggested-by: David Sterba <dsterba@suse.cz>
Link: https://lore.kernel.org/lkml/20210728092323.GW5047@twin.jikos.cz/
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210806215112.2874773-1-keescook@chromium.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>