net sampling: drop reference to a non-existing function

Due to a sloppy backport of commit 1081e76, I have introduced to the
stable ovirt-3.4 branch a call to the vlanSpeed function, which was
never defined there (It was introduced in 386f9069d3, and was not
backported)

In my verification of the patch, I did not try a host with vlan devices,
so I failed to recognise the bug.

Change-Id: I01ee0fa79c77bbd33bf9d0cbf6bdfed13c8abe95
Label: ovirt-3.4-only
Bug-Url: https://bugzilla.redhat.com/1121643
Signed-off-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/30547
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Ondřej Svoboda <osvoboda@redhat.com>
Reviewed-by: Stanislav Mikhalevich <msio57@gmail.com>
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>