vlan.4: Canonicalize SYNOPSIS + tag SPDX

MFC after:	3 days

share/man/man4/vlan.4

@@ -1,4 +1,6 @@
 .\"
+.\" SPDX-License-Identifier: BSD-2-Clause
+.\"
 .\" Copyright (c) 2001 Yar Tikhiy
 .\" All rights reserved.
 .\"
@@ -28,21 +30,13 @@
 .Os
 .Sh NAME
 .Nm vlan
-.Nd "IEEE 802.1Q VLAN network interface"
+.Nd IEEE 802.1Q VLAN network interface
 .Sh SYNOPSIS
-To compile this driver into the kernel,
-place the following line in your
-kernel configuration file:
-.Bd -ragged -offset indent
-.Cd "device vlan"
-.Ed
+.Cd device vlan
 .Pp
-Alternatively, to load the driver as a
-module at boot time, place the following line in
+In
 .Xr loader.conf 5 :
-.Bd -literal -offset indent
-if_vlan_load="YES"
-.Ed
+.Cd if_vlan_load="YES"
 .Sh DESCRIPTION
 The
 .Nm