mac80211: add iw command wrapper with error logging

Currently it's close to impossible to tell what part of mac80211 setup
went wrong. Errors logged into system log look like this:
radio0 (6155): command failed: No error information (-524)
radio0 (6155): command failed: Not supported (-95)
radio0 (6155): command failed: I/O error (-5)
radio0 (6155): command failed: Too many open files in system (-23)

With this commit change it's getting clear:
command failed: No error information (-524)
Failed command: iw dev wlan0 del
command failed: Not supported (-95)
Failed command: iw phy phy0 set antenna_gain 0
command failed: I/O error (-5)
Failed command: iw phy phy0 set distance 0
command failed: Too many open files in system (-23)
Failed command: iw phy phy0 interface add wlan0 type __ap

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

package/kernel/mac80211/files/lib/netifd/wireless/mac80211.sh

@@ -14,6 +14,10 @@ MP_CONFIG_INT="mesh_retry_timeout mesh_confirm_timeout mesh_holding_timeout mesh
 MP_CONFIG_BOOL="mesh_auto_open_plinks mesh_fwding"
 MP_CONFIG_STRING="mesh_power_mode"
 
+iw() {
+	command iw $@ || logger -t mac80211 "Failed command: iw $@"
+}
+
 drv_mac80211_init_device_config() {
 	hostapd_common_add_device_config