brcm47xx: migrate basic network settings from old releases

brcm47xx: migrate basic network settings from old releases

Old OpenWrt releases were using network configs that are not valid
anymore. They were specifying ports tagging in a different way (or were
not tagging CPU at all) and were using VID 0 which is a reserved value.

Modifying network configuration to apply all needed changes would be
pretty tricky. Script /etc/init.d/netconfig that generates new config is
quite complex itself.
So instead let's save the most important settings, regenerate config
from the scratch and restore values. This should work for 99% of users.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
SVN-Revision: 41500