Remove mac address from host interface statistics

It's unnecessary to report mac address in host interface statistics
since it's unchanged. And it's not used by engine side. So it's safe
to remove it.

Change-Id: If5c2b455387f30bfb386662fa040a82b051f153d
Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/13840
Reviewed-by: Petr Šebek <psebek@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>