show port error disable state in device ports view

lib/App/Netdisco/DB/Result/DevicePort.pm

@@ -175,8 +175,7 @@ device port.
 
 __PACKAGE__->might_have( properties => 'App::Netdisco::DB::Result::DevicePortProperties', {
   'foreign.ip' => 'self.ip', 'foreign.port' => 'self.port',
-  }, { join_type => 'LEFT OUTER' }
-);
+});
 
 =head2 ssid
 
@@ -308,6 +307,15 @@ ID assigned to untagged frames received on the port).
 
 sub native { return (shift)->vlan }
 
+=head2 error_disable_cause
+
+Returns the textual reason given by the device if the port is in an error
+state, or else `undef` if the port is not in an error state.
+
+=cut
+
+sub error_disable_cause { return (shift)->get_column('properties_error_disable_cause') }
+
 =head2 vlan_count
 
 Returns the number of VLANs active on this device port. Enable this column by