selftests: forwarding: Allow importing dependent libraries

The next patch introduces a new mlxsw-specific test that uses
mirror_gre_lib.sh and mirror_gre_topo_lib.sh.

However when sourcing their own deps, these libraries assume that the
test that's running is in the same directory. That's not the case for
driver-specific tests.

So change the libraries to source their deps through $relative_path.
That variable is set up by lib.sh, which should be imported by the test
in question in any case.
Signed-off-by: NPetr Machata <petrm@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

tools/testing/selftests/net/forwarding/mirror_gre_lib.sh

 # SPDX-License-Identifier: GPL-2.0
 
-source mirror_lib.sh
+source "$relative_path/mirror_lib.sh"
 
 quick_test_span_gre_dir_ips()
 {

tools/testing/selftests/net/forwarding/mirror_gre_topo_lib.sh

@@ -33,7 +33,7 @@
 #   |                                                                         |
 #   +-------------------------------------------------------------------------+
 
-source mirror_topo_lib.sh
+source "$relative_path/mirror_topo_lib.sh"
 
 mirror_gre_topo_h3_create()
 {