Fix everflow/test_everflow_testbed.py for dualtor-aa/dualtor-aa-56 (sonic-net#17219)

What is the motivation for this PR?
Fix failures in everflow/test_everflow_testbed.py::test_everflow_frwd_with_bkg_trf is failing on dualtor-aa/dualtor-aa-56 variants
The test case brings down Bgp as part of the test. In the case of dualtor-aa/dualtor-aa-56, this causes the selected ToR on which Everflow is configured to transition into a standby ToR, affecting upstream and downstream test traffic flows.
In active-active dualtor topology variants, upstream traffic from the server can land on either of the ToRs - given we configure the Everflow rules on a single ToR, we want the traffic stream to always land on the selected ToR. This can be done by setting up the unselected ToR as the standby
How did you do it?
Calling fixtures "toggle_all_simulator_ports_to_rand_selected_tor" and "setup_standby_ports_on_rand_unselected_tor_unconditionally" in def test_everflow_frwd_with_bkg_tr will ensure that the selected ToR configured for Everflow will always be the active ToR

How did you verify/test it?
Ran everflow/test_everflow_testbed.py::test_everflow_frwd_with_bkg_trf on DCS-7260CX3 and DCS-7050CX3

Author: pragnya-arista

tests/everflow/test_everflow_testbed.py

@@ -666,7 +666,8 @@ def test_everflow_frwd_with_bkg_trf(self,
                                         setup_info,  # noqa F811
                                         setup_mirror_session,
                                         dest_port_type, ptfadapter, tbinfo,
-                                        erspan_ip_ver):  # noqa F811
+                                        erspan_ip_ver, toggle_all_simulator_ports_to_rand_selected_tor,  # noqa F811
+                                        setup_standby_ports_on_rand_unselected_tor_unconditionally):  # noqa F811
         """
         Verify basic forwarding scenarios for the Everflow feature with background traffic.
         Background Traffic PKT1 IP in IP with same ports & macs but with dummy ips