brcm47xx: fix switch handling

This fixes some problems with the switch handling

 * It now send the messages again to indicate a button for failsafe mode should be pressed
 * it does not leak packages between wan and lan any more
 * the switch works again in normal mode

The Ethernet connection has to be up when the switch driver switch-robo 
is insmoded therefor we just do it again.
Explicitly set enable_vlan to prevent leaking packages.

This should close #13869, #13868 and #13716


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37286 3c298f89-4303-0410-b956-a3cf2f4a3e73