Merge branch 'Add-a-mlxsw-specific-test-for-mirror-to-gretap'

Petr Machata says:

====================
Add a mlxsw-specific test for mirror-to-gretap

Some configurations of mirror-to-gretap are impossible for mlxsw to
offload. Add a test that checks that these out-of-domain conditions are
handled properly by mlxsw.

In patch #1, fix mirror_gre_lib.sh and mirror_gre_topo_lib.sh so that
they can be imported from directories other than forwarding/.

In patch #2, add a test to check handling of several scenarios that
mlxsw is expected to fail to offload.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>