cfg80211: constify wowlan/coalesce mask/pattern pointers

This requires changing the nl80211 parsing code a bit to use
intermediate pointers for the allocation, but clarifies the
API towards the drivers.

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

include/net/cfg80211.h

@@ -1827,7 +1827,7 @@ struct cfg80211_pmksa {
  * memory, free @mask only!
  */
 struct cfg80211_pkt_pattern {
-	u8 *mask, *pattern;
+	const u8 *mask, *pattern;
 	int pattern_len;
 	int pkt_offset;
 };