If the expected throughput is queried before rate control has been
initialized, the minstrel op for it will crash while trying to access
the rate table.
Check for WLAN_STA_RATE_CONTROL before attempting to use the rate
control op.
Reported-by: Jean-Pierre Tosoni <jp.tosoni@acksys.fr>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>