bridge_opts: Add iproute2 configurator support

This patch implements bridging option setting for the iproute2
configurator (after the previous patch added it for the ifcfg
configurator).

Implementing this allows the user of the iproute2 configurator
to set bridge options like 'forward_delay=2000 multicast_snooping=0'

Change-Id: I424676a5c26250fe115a73e745199b5532f71a48
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/26762
Reviewed-by: Dan Kenigsberg <danken@redhat.com>