ipwrapper: fix Link's fromText mtu and vlanid types

Accross the codebase mtu and vlanid are specified to be integers.
This patch makes sure that when we get the information from
parsing iproute2 the types are correct.

Change-Id: I1a27e443911d7828afacb28a9bd914b6da2cdc4b
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/23275
Reviewed-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>