Only remove dhcp source routing if the removal reason is "STOP"

If the reason is FAIL then the IP configuration is not lost
and source routing should not be removed. Only STOP actually
removes the ip configuration from the device.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=995142
Change-Id: Ie92a4b4a95e9f1a7855f3d276b4e4d5b8b4c6ad3
Signed-off-by: Assaf Muller <amuller@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17961
Reviewed-by: Saggi Mizrahi <smizrahi@redhat.com>
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17963