[NET]: Increase default IFB device count.

The most usable number of ifb devices is 2. Change the default to 2.

Signed-off-by: Richard Lucassen <spamtrap@lucassen.org>
Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>