debian: Install correct vtep-ctl.

The previous syntax installed the libtool wrapper script instead of the
actual binary.  This fixes the problem.

CC: James Page <james.page@ubuntu.com>
Fixes: 3d8dede ("debian: Rationalize packaging using new debhelper.")
Reported-by: hubo <hubo@jiedaibao.com>
Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2018-October/047625.html
Acked-by: Justin Pettit <jpettit@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>

debian/openvswitch-vtep.install

@@ -1,3 +1,3 @@
 usr/share/openvswitch/scripts/ovs-vtep
 usr/share/openvswitch/vtep.ovsschema
-vtep/vtep-ctl usr/bin
+usr/bin/vtep-ctl