selftests: forwarding: mirror_gre_nh: Unset rp_filter on host VRF

The mirrored packets arrive at $h3 encapsulated in GRE/IPv4, with IP
address from 192.0.2.128/28 network. However the interface is configured
as a member of 192.0.2.160/28 and there's no route directing traffic
from the former network through that interface. Correspondingly, the RP
filter on the VRF rejects it.

Therefore turn off the VRF's RP filter.

Signed-off-by: Petr Machata <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

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

···
 	vrf_prepare
 	mirror_gre_topo_create
 
+	sysctl_set net.ipv4.conf.v$h3.rp_filter 0
+
 	ip address add dev $swp3 192.0.2.161/28
 	ip address add dev $h3 192.0.2.162/28
 	ip address add dev gt4 192.0.2.129/32
···
 
 	ip address del dev $h3 192.0.2.162/28
 	ip address del dev $swp3 192.0.2.161/28
+
+	sysctl_restore net.ipv4.conf.v$h3.rp_filter 0
 
 	mirror_gre_topo_destroy
 	vrf_cleanup