init-ifupdown: fix the networking service failure

init-ifupdown: fix the networking service failure

* Add RDEPENDS on 'ifupdown' because:
    The 'ifup' command provided by 'busybox' and 'ifupdown' behave differently
    when an interface has been configured:

    - The one from busybox
    $ sudo ifup lo; echo $?
    RTNETLINK answers: File exists
    1

    - The one from ifupdown
    $ sudo ifup lo; echo $?
    ifup: interface lo already configured
    0

    The exit code 1 from the busybox one would cause the networking service
    failed, so add RDEPENDS on ifupdown to avoid using the one from busybox.

* Do not auto config eth0 since it may not exist.

Issue-ID: INF-192

Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Change-Id: I5d9478ca163d90da3106ecf6a05ee9459df83502