Document the missing ignore_broadcast_ssid network profile parameter

Copy parameter description from hostapd.conf.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>

wpa_supplicant/wpa_supplicant.conf

@@ -843,6 +843,16 @@ fast_reauth=1
 # bssid: BSSID (optional); if set, this network block is used only when
 #	associating with the AP using the configured BSSID
 #
+# ignore_broadcast_ssid: SSID broadcast behavior
+# Send empty SSID in beacons and ignore probe request frames that do not
+# specify full SSID, i.e., require stations to know SSID.
+# default: disabled (0)
+# 1 = send empty (length=0) SSID in beacon and ignore probe request for
+#     broadcast SSID
+# 2 = clear SSID (ASCII 0), but keep the original length (this may be required
+#     with some clients that do not support empty SSID) and ignore probe
+#     requests for broadcast SSID
+#
 # priority: priority group (integer)
 # By default, all networks will get same priority group (0). If some of the
 # networks are more desirable, this field can be used to change the order in