Prettify/simplify netinfo.py:get()

get() now iterates over the links once instead of 4 times.

Change-Id: I70379b24084fa8bec88425de9eca106e2a6ae8f0
Signed-off-by: Assaf Muller <amuller@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/21652
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>