bug in default interface number computation

[Guillaume Rousse <Guillaume.Rousse@inria.fr>]

Hello.

The network-bridge script tries to automatically find the default
network interface number with the following ligne:
vifnum=${vifnum:-$(ip route list | awk '/^default / { print $NF }' | sed
's/^[^0-9]*//')}

However, this fails on mandriva, because the parsed line is:
default via 193.55.250.126 dev eth0  metric 10

This causes many troubles, such as:
http://article.gmane.org/gmane.comp.emulators.xen.user/17846

A simple solution is to change the position-based parsing to something
more robust:
vifnum=${vifnum:-$(ip route list 0.0.0.0/0 | sed 's/.*dev
[^0-9]\+\([0-9]\+\).*$/\1/')}

This is also more robust against default interfaces that would be named
otherwise as dev[0-9].