interfaces: fix a crash report

src/etc/inc/interfaces.inc

@@ -4520,22 +4520,12 @@ function get_interface_mac($interface)
     return $macinfo["macaddr"];
 }
 
-/****f* interfaces/is_jumbo_capable
- * NAME
- *   is_jumbo_capable - Test if interface is jumbo frame capable.  Useful for determining VLAN capability.
- * INPUTS
- *   $int             - string containing interface name
- * RESULT
- *   boolean          - true or false
- ******/
 function is_jumbo_capable($iface)
 {
     $intf_details = legacy_interface_details(trim($iface));
-    if (in_array('vlan_mtu', $intf_details['capabilities'])) {
-        return true;
-    } else {
-        return false;
-    }
+
+    return isset($intf_details['capabilities']) &&
+        in_array('vlan_mtu', $intf_details['capabilities']);
 }
 
 function get_vip_descr($ipaddress)

src/etc/inc/interfaces.lib.inc

@@ -199,19 +199,21 @@ function legacy_interface_stats($ifs=null)
  * @param $intf filter on interface name (empty for all)
  * @return array list of interface specifics indexed by physical interface name
  */
-function legacy_interfaces_details($intf=null)
+function legacy_interfaces_details($intf = null)
 {
     $result = array();
+
     if (!empty($intf)) {
         $tmp_intf = escapeshellarg($intf);
     } else {
-        $tmp_intf = "";
+        $tmp_intf = '';
     }
+
     $cmd = '/sbin/ifconfig -m ' . $tmp_intf;
     exec($cmd . ' 2>&1', $ifconfig_data, $ret);
     if ($ret) {
-        log_error('The command `' . $cmd . '\' failed to execute ' . implode(' ', $ifconfig_data) );
-        return array();
+        log_error('The command `' . $cmd . '\' failed to execute ' . implode(' ', $ifconfig_data));
+        return $result;
     }
 
     $current_interface = null;