ipwrapper: switch link polling to netlink

Getting the links from iproute2 implied creating a process each time
and then parsing the output. Due to the fact that this opearations
happen periodically and sometimes several times per second, the cost
was too high.

Change-Id: I09a120155e3c5be15c237171620e5c996c2af681
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/23248
Reviewed-by: Dan Kenigsberg <danken@redhat.com>