wireless: make TU conversion macros available

A few places in the code (mac80211 and iwlmvm) use the same
TU_TO_JIFFIES() macro and could use TU_TO_EXP_TIME() that
mac80211 has. Make these available to everyone and use them.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/linux/ieee80211.h

@@ -2288,4 +2288,8 @@ static inline bool ieee80211_check_tim(const struct ieee80211_tim_ie *tim,
 	return !!(tim->virtual_map[index] & mask);
 }
 
+/* convert time units */
+#define TU_TO_JIFFIES(x)	(usecs_to_jiffies((x) * 1024))
+#define TU_TO_EXP_TIME(x)	(jiffies + TU_TO_JIFFIES(x))
+
 #endif /* LINUX_IEEE80211_H */