interfaces: optionally allow to set txpower

PR: https://forum.opnsense.org/index.php?topic=3462.0
(cherry picked from commit 3da906b6)

src/etc/inc/interfaces.inc

@@ -2293,10 +2293,6 @@ function interface_wireless_configure($if, &$wl, &$wlcfg)
         $wlcmd[] = "-mediaopt turbo";
     }
 
-    /* handle txpower setting */
-    /* if($wlcfg['txpower'] <> "")
-        $wlcmd[] = "txpower " . escapeshellarg($wlcfg['txpower']);
-    */
     /* handle wme option */
     if (isset($wlcfg['wme']['enable'])) {
         $wlcmd[] = "wme";
@@ -2579,6 +2575,10 @@ EOD;
     mwexec("/sbin/ifconfig " . escapeshellarg($if) . " " . $wlcmd_args, false);
     unset($wlcmd_args, $wlcmd);
 
+    /* configure txpower setting (it has been known to fail so run it separately) */
+    if (!empty($wlcfg['txpower'])) {
+        mwexecf('/sbin/ifconfig %s txpower %s', array($if, $wlcfg['txpower']));
+    }
 
     sleep(1);
     /* execute hostapd and wpa_supplicant if required in shell */

src/www/interfaces.php

@@ -2792,9 +2792,10 @@ include("head.inc");
                           <td><a id="help_for_txpower" href="#" class="showhelp"><i class="fa fa-info-circle"></i></a> <?=gettext("Transmit power"); ?></td>
                           <td>
                             <select name="txpower" class="selectpicker" data-size="10" data-style="btn-default" id="txpower">
+                              <option value=""><?= gettext('default') ?></option>
 <?php
                             for($x = 99; $x > 0; $x--):?>
-                              <option value="<?=$x;?>" <?=$pconfig["txpower"] == $x ? "selected=\"selected\"" : "";?> ><?=$x;?></option>
+                              <option value="<?=$x;?>" <?=$pconfig['txpower'] == $x ? 'selected="selected"' : '';?>><?=$x;?></option>
 <?php
                               endfor;?>
                             </select>