mac80211: recalculate min channel width on VHT opmode changes

mac80211: recalculate min channel width on VHT opmode changes

[ Upstream commit d2941df8fbd9708035d66d889ada4d3d160170ce ]

When an associated station changes its VHT operating mode this
can/will affect the bandwidth it's using, and consequently we
must recalculate the minimum bandwidth we need to use. Failure
to do so can lead to one of two scenarios:
 1) we use a too high bandwidth, this is benign
 2) we use a too narrow bandwidth, causing rate control and
    actual PHY configuration to be out of sync, which can in
    turn cause problems/crashes

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>