Delay switch(4) interface start up so it can attach virtual interfaces

like vether(4).
nits from and ok benno@, phessler@

src/etc/netstart

@@ -1,6 +1,6 @@
 #!/bin/sh -
 #
-#	$OpenBSD: netstart,v 1.170 2016/09/09 19:48:16 jasper Exp $
+#	$OpenBSD: netstart,v 1.171 2016/09/27 09:19:11 rzalamena Exp $
 
 # Turn off Strict Bourne shell mode.
 set +o sh
@@ -251,7 +251,7 @@ fi
 
 # Configure all the non-loopback interfaces which we know about, but
 # do not start interfaces which must be delayed. Refer to hostname.if(5)
-ifmstart "" "trunk svlan vlan carp gif gre pfsync pppoe tun bridge pflow"
+ifmstart "" "trunk svlan vlan carp gif gre pfsync pppoe tun bridge switch pflow"
 
 # The trunk interfaces need to come up first in this list.
 # The (s)vlan interfaces need to come up after trunk.
@@ -283,7 +283,7 @@ fi
 # require routes to be set. TUN might depend on PPPoE, and GIF or GRE may
 # depend on either of them. PFLOW might bind to ip addresses configured
 # on either of them.
-ifmstart "pppoe tun gif gre bridge pflow"
+ifmstart "pppoe tun gif gre bridge switch pflow"
 
 # Reject 127/8 other than 127.0.0.1.
 route -qn add -net 127 127.0.0.1 -reject >/dev/null