configNetwork: Fix bootproto preservation for bridgeless network

bootproto should be also preserved for bridgeless network as what
the commit 948057 fixed for static ip address.

Change-Id: Ie8bb5fd9fc6ad69cf120d62264d73490b65b82d7
Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/11356
Reviewed-by: Hunt Xu <mhuntxu@gmail.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>