cfg80211: validate remain-on-channel time better

The remain-on-channel time validation shouldn't
depend on the value of HZ, as it does now with
the check against jiffies, since then you might
use a value that works on one system but not on
another. Fix it by checking against a minimum
that's fixed.

Also add validation of the wait duration for a
management frame TX since this also translates
into remain-on-channel internally.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/linux/nl80211.h

@@ -1522,6 +1522,8 @@ enum nl80211_attrs {
 #define NL80211_MAX_NR_CIPHER_SUITES		5
 #define NL80211_MAX_NR_AKM_SUITES		2
 
+#define NL80211_MIN_REMAIN_ON_CHANNEL_TIME	10
+
 /**
  * enum nl80211_iftype - (virtual) interface types
  *