cfg80211: add more comments for ap_isolate in bss_parameters

The value of struct bss_parameters::ap_isolate will be -1, 0 or 1.
The value -1 means not to change. To prevent developers from thinking
ap_isolate is only 0 or 1, I add more comments on it.
Signed-off-by: Wright Feng <wright.feng@cypress.com>
Reviewed-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200908060157.98846-1-wright.feng@cypress.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/cfg80211.h

@@ -1787,6 +1787,7 @@ struct mpath_info {
  *	(or NULL for no change)
  * @basic_rates_len: number of basic rates
  * @ap_isolate: do not forward packets between connected stations
+ *	(0 = no, 1 = yes, -1 = do not change)
  * @ht_opmode: HT Operation mode
  *	(u16 = opmode, -1 = do not change)
  * @p2p_ctwindow: P2P CT Window (-1 = no change)