selftests: srv6: make srv6_end_dt46_l3vpn_test more robust

On some distributions, the rp_filter is automatically set (=1) by
default on a netdev basis (also on VRFs).
In an SRv6 End.DT46 behavior, decapsulated IPv4 packets are routed using
the table associated with the VRF bound to that tunnel. During lookup
operations, the rp_filter can lead to packet loss when activated on the
VRF.
Therefore, we chose to make this selftest more robust by explicitly
disabling the rp_filter during tests (as it is automatically set by some
Linux distributions).

Fixes: 03a0b567 ("selftests: seg6: add selftest for SRv6 End.DT46 Behavior")
Reported-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Andrea Mayer <andrea.mayer@uniroma2.it>
Tested-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/srv6_end_dt46_l3vpn_test.sh

@@ -292,6 +292,11 @@ setup_hs()
 	ip netns exec ${hsname} sysctl -wq net.ipv6.conf.all.accept_dad=0
 	ip netns exec ${hsname} sysctl -wq net.ipv6.conf.default.accept_dad=0
 
+	# disable the rp_filter otherwise the kernel gets confused about how
+	# to route decap ipv4 packets.
+	ip netns exec ${rtname} sysctl -wq net.ipv4.conf.all.rp_filter=0
+	ip netns exec ${rtname} sysctl -wq net.ipv4.conf.default.rp_filter=0
+
 	ip -netns ${hsname} link add veth0 type veth peer name ${rtveth}
 	ip -netns ${hsname} link set ${rtveth} netns ${rtname}
 	ip -netns ${hsname} addr add ${IPv6_HS_NETWORK}::${hs}/64 dev veth0 nodad
@@ -316,11 +321,6 @@ setup_hs()
 	ip netns exec ${rtname} sysctl -wq net.ipv6.conf.${rtveth}.proxy_ndp=1
 	ip netns exec ${rtname} sysctl -wq net.ipv4.conf.${rtveth}.proxy_arp=1
 
-	# disable the rp_filter otherwise the kernel gets confused about how
-	# to route decap ipv4 packets.
-	ip netns exec ${rtname} sysctl -wq net.ipv4.conf.all.rp_filter=0
-	ip netns exec ${rtname} sysctl -wq net.ipv4.conf.${rtveth}.rp_filter=0
-
 	ip netns exec ${rtname} sh -c "echo 1 > /proc/sys/net/vrf/strict_mode"
 }