hostapd: explicitly set beacon interval for wpa_supplicant

The beacon_int is currently set explicitly for hostapd and when LEDE uses
iw to join and IBSS/mesh. But it was not done when wpa_supplicant was used
to join an encrypted IBSS or mesh.

This configuration is required when an AP interface is configured together
with an mesh interface. The beacon_int= line must therefore be re-added to
the wpa_supplicant config. The value is retrieved from the the global
variable.

Fixes: 1a16cb9 ("mac80211, hostapd: always explicitly set beacon interval")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name> [rebase]
(cherry picked from commit 772afef)

package/network/services/hostapd/files/hostapd.sh

@@ -723,6 +723,7 @@ wpa_supplicant_add_network() {
 	}
 	local beacon_int brates mrate
 	[ -n "$bssid" ] && append network_data "bssid=$bssid" "$N$T"
+	[ -n "$beacon_int" ] && append network_data "beacon_int=$beacon_int" "$N$T"
 
 	local bssid_blacklist bssid_whitelist
 	json_get_values bssid_blacklist bssid_blacklist