[source] hostapd: add support for acs_chan_bias option

[LEDE Commits]

hauke pushed a commit to source.git, branch master:
https://git.lede-project.org/4ed40be3e32643560874688d34b6fc69e6c4d20d

commit 4ed40be3e32643560874688d34b6fc69e6c4d20d
Author: Kevin Darbyshire-Bryant <kevin at darbyshire-bryant.me.uk>
AuthorDate: Thu Jun 15 12:48:56 2017 +0100

    hostapd: add support for acs_chan_bias option
    
    During auto channel selection we may wish to prefer certain channels
    over others.
    
    e.g. we can just squeeze 4 channels into europe so '1:0.8 5:0.8 9:0.8
    13:0.8' does that.
    
    Signed-off-by: Kevin Darbyshire-Bryant <kevin at darbyshire-bryant.me.uk>
---
 package/network/services/hostapd/Makefile         | 2 +-
 package/network/services/hostapd/files/hostapd.sh | 6 +++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/package/network/services/hostapd/Makefile b/package/network/services/hostapd/Makefile
index b7cc6b9..8a1f083 100644
--- a/package/network/services/hostapd/Makefile
+++ b/package/network/services/hostapd/Makefile
@@ -7,7 +7,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=hostapd
-PKG_RELEASE:=3
+PKG_RELEASE:=4
 
 PKG_SOURCE_URL:=http://w1.fi/hostap.git
 PKG_SOURCE_PROTO:=git
diff --git a/package/network/services/hostapd/files/hostapd.sh b/package/network/services/hostapd/files/hostapd.sh
index 86e9a32..2c015f9 100644
--- a/package/network/services/hostapd/files/hostapd.sh
+++ b/package/network/services/hostapd/files/hostapd.sh
@@ -66,6 +66,8 @@ hostapd_common_add_device_config() {
 	config_add_string require_mode
 	config_add_boolean legacy_rates
 
+	config_add_string acs_chan_bias
+
 	hostapd_add_log_config
 }
 
@@ -76,7 +78,7 @@ hostapd_prepare_device_config() {
 	local base="${config%%.conf}"
 	local base_cfg=
 
-	json_get_vars country country_ie beacon_int:100 doth require_mode legacy_rates
+	json_get_vars country country_ie beacon_int:100 doth require_mode legacy_rates acs_chan_bias
 
 	hostapd_set_log_options base_cfg
 
@@ -93,6 +95,8 @@ hostapd_prepare_device_config() {
 		[ "$hwmode" = "a" -a "$doth" -gt 0 ] && append base_cfg "ieee80211h=1" "$N"
 	}
 
+	[ -n "$acs_chan_bias" ] && append base_cfg "acs_chan_bias=$acs_chan_bias" "$N"
+
 	local brlist= br
 	json_get_values basic_rate_list basic_rate
 	local rlist= r