load_needed_modules: adding bridge module

if bridge module is not loaded
net.bridge.bridge-nf-call-* is ignored by sysctl.

Change-Id: I03a6bf5d93060105de9ad1d4d4d89d119913c98c
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/11610
Reviewed-by: Dan Kenigsberg <danken@redhat.com>