nl80211: fix NL80211_FEATURE_P2P_DEVICE_NEEDS_CHANNEL API

My commit removing that also removed it from the header file
which can break compilation of userspace that needed it, add
it back for API/ABI compatibility purposes (but no code to
implement anything for it.)
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/uapi/linux/nl80211.h

@@ -3856,6 +3856,8 @@ enum nl80211_ap_sme_features {
  * @NL80211_FEATURE_CELL_BASE_REG_HINTS: This driver has been tested
  *	to work properly to suppport receiving regulatory hints from
  *	cellular base stations.
+ * @NL80211_FEATURE_P2P_DEVICE_NEEDS_CHANNEL: (no longer available, only
+ *	here to reserve the value for API/ABI compatibility)
  * @NL80211_FEATURE_SAE: This driver supports simultaneous authentication of
  *	equals (SAE) with user space SME (NL80211_CMD_AUTHENTICATE) in station
  *	mode
@@ -3897,7 +3899,7 @@ enum nl80211_feature_flags {
 	NL80211_FEATURE_HT_IBSS				= 1 << 1,
 	NL80211_FEATURE_INACTIVITY_TIMER		= 1 << 2,
 	NL80211_FEATURE_CELL_BASE_REG_HINTS		= 1 << 3,
-	/* bit 4 is reserved - don't use */
+	NL80211_FEATURE_P2P_DEVICE_NEEDS_CHANNEL	= 1 << 4,
 	NL80211_FEATURE_SAE				= 1 << 5,
 	NL80211_FEATURE_LOW_PRIORITY_SCAN		= 1 << 6,
 	NL80211_FEATURE_SCAN_FLUSH			= 1 << 7,