ipwrapper: add convenient Link.isNICLike

The addition of Link.isNICLike() allows us to centralize the logic
for which devices are to be treated as nics.

Change-Id: If641d0b8a72f069ec47dcb18b68cac2fbd8a498f
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/21562
Reviewed-by: Dan Kenigsberg <danken@redhat.com>