selftests: openvswitch: Support explicit tunnel port creation.

The OVS module can operate in conjunction with various types of
tunnel ports.  These are created as either explicit tunnel vport
types, OR by creating a tunnel interface which acts as an anchor
for the lightweight tunnel support.

This patch adds the ability to add tunnel ports to an OVS
datapath for testing various scenarios with tunnel ports.  With
this addition, the vswitch "plumbing" will at least be able to
push packets around using the tunnel vports.  Future patches
will add support for setting required tunnel metadata for lwts
in the datapath.  The end goal will be to push packets via these
tunnels, and will be used in an upcoming commit for testing the
path MTU.

Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Simon Horman <horms@kernel.org>
Signed-off-by: Aaron Conole <aconole@redhat.com>
Link: https://patch.msgid.link/20240625172245.233874-2-aconole@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>